Donald Trump has a huge campaign war chest and a vast, aggressive digital operation. And the US economy has shown stubborn resilience throughout the president’s three years in office, keeping unemployment levels low and stock markets high.

But as they seek to oust Trump in 2020’s election what most worries many top Democrats is what’s shaping up in their own party: an extended Democratic primary resulting in a fractured party struggling to rally around the eventual nominee.

That’s the overall sentiment of Democrats based on interviews with over a dozen senior party figures – including ex-mayors and former governors – and top strategists during a chaotic month in the Democratic primary leading up to the Iowa caucuses.

Recent polling has shown the progressive senator Bernie Sanders surging in Iowa, to the chagrin of centrist Democratic leaders who hoped a candidate like former vice-president Joe Biden or even the young and charismatic former South Bend, Indiana, mayor Pete Buttigieg might score an early win.

Even though the field has now shrunk from two dozen candidates, Democrats are increasingly expecting a drawn-out primary with deep-pocketed frontrunners bashing each other and long-shot candidates refusing to drop out, further splintering the vote and leaving scars that will last in the general election.

“I think this is going to be a longer, more protracted primary fight and we’re going to have certainly weeks, if not months where we’ll be doing our primary and we won’t be talking to swing voters in, say, Tampa Bay,” warned Florida-based Democratic strategist Scott Arceneaux.

Despite this strategists and veteran lawmakers from across the political spectrum of the Democratic party expressed strong confidence that there is still an opening to oust Trump from office.

“I’m still very bullish on 2020. I think Trump’s going to have a very difficult time winning re-election,” said the former Virginia governor Terry McAuliffe.

But no one is taking victory for granted. The almost universal sentiment shared by those the Guardian spoke to is that Democrats could also be in the process of shooting themselves in the foot.

“The most important thing for people reading to come away with is that we can lose this election,” said a top adviser for a former 2020 Democratic candidate.

Money money money!

There’s plenty of reason for Democrats to worry about money. Donald Trump has raised over $100m already with effectively no real opposition within the Republican primary.

“I think someone who’s not worried about the money is crazy. Trump’s sitting on $100m right now and we’re nowhere close to having a nominee and they will be able to raise money but we’re still so fractured,” said Democratic consultant Brandon Hall. “That worries me. I mean I don’t know how that doesn’t worry everybody, that we’re always going to be playing catchup on the money.”

But others argue the question isn’t whether Democrats will be able to raise money competitively, it’s when they’ll be able to raise that money. After an exhausting primary, Trump will be able to just dump money against the newly minted nominee, warned the former Chicago mayor Rahm Emanuel. That nominee will have to immediately start fundraising again to catch up to the war chest Trump had been hoarding away.

“I don’t think it’s going to be hard to raise all the money you need but that early advantage is not inconsequential given that this is coming down to a few voters in a few states,” Emanuel said.

Trump’s digital operation

A staple of the Trump re-election campaign has been its large digital operation. A Guardian analysis found that Trump’s re-election campaign has already spent $20m on more than 218,000 Facebook ads. And Democrats have noticed.

“On the digital side Trump’s digital operation is two things: smart and dangerous,” said Democratic strategist Jennifer Holdsworth. “It’s both. So I think that we are playing checkers and they’re playing chess in that particular lane of strategy and it’s something we are not going to wake up to until we’ve gotten past the primary and they are miles ahead in terms of messaging and we’re going to have to catch up.

That’s why, Holdsworth continued, Democrats needed to quickly rally around the eventually nominee “either before or immediately after the convention or we’re never going to catch up”.

Incumbency and what history tells us: Trump is strong

By the traditional metrics on which an incumbent’s re-election chances are usually judged, Trump should be viewed as unbeatable. Unemployment remains low. During the Trump administration US special forces killed the Islamic State leader Abu Bakr al-Baghdadi. Democrats control only one chamber of Congress. And Trump’s approval rating within the Republican party remains sky high.

But Trump is a divisive figure, to put it mildly. Democrats point to their gains in suburban districts across the country and flipping seven governor’s mansions in the 2018 midterm elections. They see that as a herald of Democratic competitiveness in Republican-leaning parts of the country. Democratic strategists hope fatigue from seemingly daily national crises will see reluctant moderates and swing voters vote Trump out of office.

Emanuel said the deciding issues will be the key aspects of the economy versus a set of issues Democrats have run and won on in recent years.

“He’s got three and a half per cent unemployment. Three per cent real wage growth. And three per cent real home value growth,” Emanuel said. “And our threes are the three Hs: healthcare, higher education, housing. Meaning we’re going to emphasize the challenges, crises in those three areas.”

Trump will argue “everything’s copacetic,” Emanuel added. “And it’s really those three economics against each other.”

The Democratic primary: no end in sight

The most persistent source of Democratic handwringing is a traditional aspect of any presidential cycle: the months-long primary where fellow candidates turn on each other. After months of relatively respectful campaigning, the knives are finally coming out just before the first vote in Iowa next week.

“Trump has had an incredible advantage as the incumbent and has been effectively running a general election campaign online and off since he was inaugurated and so the sooner we have a nominee that we can consolidate resources and momentum and energy around, the sooner his advantage will diminish in the race,” said Tara McGowan, co-founder of the progressive political not-for-profit group Acronym.

Former vice-president Joe Biden and Senator Bernie Sanders have been trading blows over social security and electability. Buttigieg has unsubtly been contrasting his youth and novelty with the competitors who have been in politics for years. In one of the most heated exchanges the detente between Sanders and Senator Elizabeth Warren morphed into a red-hot rivalry when Warren said that during a closed-door meeting Sanders had told her a woman could not win the 2020 election.

Running out of money – and a brokered convention?

All four top-tier candidates have deep war chests, allowing them to continue campaigning – and fighting each other – far into 2020.

“The thing that I would be most concerned about would be is if we don’t lock down this nomination and we allow it to go on all the way to the convention,” McAuliffe said. “That would make it more problematic. We’ve got to build a field operation in all of these states and get them staffed and up and running.”

Democrats worry a long, bloody primary could advantage Trump. It could also drain Democrats’ resources.

“The exhaustion, not that Trump has too much money but that the Democrats have spent all of theirs,” said the former California governor Jerry Brown. “That’s possible.”

Senior party leaders are already grumbling about the prospect of no candidate winning a decisive victory during the primaries and having a brokered convention which has to elect a nominee from its competing factions. That could push some embittered voters to sit out the general election, depending on which figure emerges as the winner.

“I’m concerned about candidates who might not win – their folks just take a pass,” Democratic strategist Amy Chapman said.

“We saw in 2016 the damaging outsized, unbelievably detrimental effect the convention had on Hillary’s candidacy into the fall,” said Holdsworth, a former executive director of the New Jersey Democratic party. “That has the potential to be just exacerbated this time around.”

Appealing to swing voters

A persistent fear throughout the Democratic primary has been picking a viable nominee. The 2020 Democratic primary has been full of ideological and policy debates over Medicare for All, immigration, a Green New Deal and whether a veteran or young charismatic leader can beat Trump.

But eclipsing all of that is worries among some party leaders that Democrats will nominate a candidate who can’t attract key swing voters. Centrist Democrats have begun to argue that if Sanders won the nomination, it would doom Democrats chances. Recently, Buttigieg’s campaign has begun sending out fundraising pitches with subject lines like “Bernie Sanders could be the nominee”.

It’s a view contested by Sanders supporters, who argue that running a centrist candidate failed to beat Trump in 2016 and that the eventual nominee’s campaign needs an energized base to beat the president’s fervent fans.

As Sanders has risen to the front of the field in Iowa and New Hampshire, Democrats have begun worrying no more moderate candidate could beat him.

“The thing that concerns me the absolute most right now is Bernie being the nominee,” a veteran Democratic strategist with ties to multiple candidates said.

Health concerns

Healthcare has been a major flashpoint within the Democratic primary. At the beginning of 2020 it seemed like any candidate who didn’t support Medicare for All wouldn’t last more than a week. Now, though, some lead candidates have argued that the proposal would alienate some crucial general election voters. It remains a contentious policy topic for Democrats.

“I think some voters look at Medicare for All and say, ‘I don’t support that plan but at least Democrats are trying to think big thoughts about how to fix the problem.’ And in reality the system will probably make it a more moderate program in the end,” said Marie Harf, the executive director of the Serve America political action committee. Harf added: “I do think the Medicare for All option is not as palatable to some voters in the general.”

The veteran Democratic strategist pointed to questions about where Warren stands on healthcare and Medicare for All. “I think Warren’s a problem. I think any candidate who would lose the healthcare debate to Trump is a problem. I think her stance is a problem. I think a lot of what’s ailing her is correctable. I think it’s not correctable with Bernie and he has no desire to correct it.”

Guy Cecil, the chairman of the Priorities USA Super Pac, said skeptics of Medicare for All worry that it will take longer and more resources to win them over with the plan.

“I think the proponents see it as an opportunity for cost as well. There’s a recognition that given how close the Senate will be, the chances of passing Medicare for All are almost nonexistent without a significant political sea change or some huge surprise in the United States Senate,” Cecil said.

“So the concern is that you’re risking with a lot of voters needing to explain why they’re taking away your private insurance. Now you can win that argument but it takes a lot of resources, a lot of focus.”

Priorities has been preparing ad campaigns and other work in case either the Democratic nominee supports Medicare for All or a different healthcare plan.

Still, more moderate Democrats remain skeptical of their options in the centrist lane of the party who advocate for less radical healthcare change. Buttigieg is too young and inexperienced, said the top adviser to a former 2020 candidate.

“I do not believe he can win a general election. One, he’s 37. Two, he’s a mayor. Three, I think,” the adviser said, adding, “If by Super Tuesday I see that things aren’t moving towards Biden I will be deeply concerned.”