Early fund-raising has given Democrats cause for optimism in key states as Republicans split over how closely to align with Donald Trump’s preferences. Six months into the Biden administration, Senate Democrats are expressing a cautious optimism that the party can keep control of the chamber in the 2022 midterm elections, enjoying large fund-raising hauls in marquee races as they plot to exploit Republican retirements in key battlegrounds and a divisive series of unsettled G.O.P. primaries.Swing-state Democratic incumbents, like Senators Raphael Warnock of Georgia and Mark Kelly of Arizona, restocked their war chests with multimillion-dollar sums ($7.2 million and $6 million, respectively), according to new financial filings this week. That gives them an early financial head start in two key states where Republicans’ disagreements over former President Donald J. Trump’s refusal to accept his loss in 2020 are threatening to distract and fracture the party.But Democratic officials are all too aware of the foreboding political history they confront: that in a president’s first midterms, the party occupying the White House typically loses seats — often in bunches. For now, Democrats hold power by only the narrowest of margins in a 50-50 split Senate, with Vice President Kamala Harris serving as the tiebreaker to push through President Biden’s expansive agenda on the economy, the pandemic and infrastructure.The midterms are still more than 15 months away, but the ability to enact new policy throughout Mr. Biden’s first term hinges heavily on his party’s ability to hold the Senate and House.Four Senate Democratic incumbents are up for re-election in swing states next year — making them prime targets for Republican gains. But in none of those four states — New Hampshire, Nevada, Arizona and Georgia — has a dominant Republican candidate emerged to consolidate support from the party’s divergent wings. Out of office and banished from social media, Mr. Trump continues to insist on putting his imprint on the party with rallies and regular missives imposing an agenda of rewarding loyalists and exacting retribution against perceived enemies. That does not align with Senate Republican strategists who are focused singularly on retaking the majority and honing messages against the Democrats who now fully control Washington.“The only way we win these races is with top-notch candidates,” said Alex Conant, a Republican strategist who used to work on Senate races. “Are Republicans able to recruit top-notch candidates in the Trump era?”Of the seven contests that political handicappers consider most competitive in 2022, all but one are in states that Mr. Biden carried last year.“We’re running in Biden country,” said Matt Canter, a Democratic pollster involved in Senate races. “That doesn’t make any of these races easy. But we’re running in Biden country.”The campaign filings this week provided an early financial snapshot of the state of play in the Senate battlefield, where the total costs could easily top $1 billion. Other than the Senate majority leader, Chuck Schumer, the top fund-raiser among all senators in the last three months was Tim Scott, Republican of South Carolina. Mr. Scott collected $9.6 million in the months after his State of the Union response, an eye-opening sum that has stoked questions about his 2024 ambitions.Senator Tim Scott of South Carolina collected $9.6 million in the months after his State of the Union response.Stefani Reynolds for The New York TimesBut critical races remain unsettled for Republicans. The party is still trying to find compelling Senate candidates in several states, with Chris Sununu, the governor of New Hampshire, considered the highest priority for recruitment, to challenge Senator Maggie Hassan, a Democrat who raised $3.25 million in the last three months. A bevy of Republican senators have lobbied Mr. Sununu to enter the race, and Senator Rick Scott of Florida, who leads the National Republican Senatorial Committee, went so far as to ask activists at a conservative conference last week to “call Chris Sununu” and urge him to run.“If he does, we will win,” Mr. Scott said.Mr. Scott has similarly pursued the former attorney general of Nevada, Adam Laxalt, saying last month that he expected Mr. Laxalt to run against Senator Catherine Cortez-Masto, the Democratic incumbent.The unexpected retirements of Republican senators in Pennsylvania and North Carolina have opened seats and opportunities for Democrats in those swing states, but the path to victory is complicated. In both, Democrats must navigate competitive primaries that pit candidates who represent disparate elements of the party’s racial and ideological coalition: Black and white; moderate and progressive; urban, suburban and more rural.In Pennsylvania, the Democratic lieutenant governor, John Fetterman, has emerged as one of the strongest fund-raising newcomers, taking in $2.5 million in the quarter. Val Arkoosh, a county commissioner in a Philadelphia suburb, raised $1 million, and Malcolm Kenyatta, a state legislator seeking to become the nation’s first openly gay Black senator, raised $500,000. Representative Conor Lamb, a moderate from outside Pittsburgh, is also considering a run.In Wisconsin, a third Republican incumbent, Senator Ron Johnson, has wavered for months over whether he will seek a third term. Mr. Johnson raised only $1.2 million in the last quarter, just enough to carry on but not quite enough to dispel questions about his intentions.Whether or not Mr. Johnson runs, Wisconsin is among the top Democratic targets in 2022 because Mr. Biden carried it narrowly in 2020. Perhaps nothing has better predicted the outcome of Senate races in recent cycles than a state’s presidential preferences.Lt. Gov. John Fetterman of Pennsylvania, a Democrat, has emerged as one of the strongest fund-raisers among newcomers as he pursues the state’s open Senate seat.Maddie McGarvey for The New York TimesIn Florida, national Democrats have all but anointed Representative Val Demings, a Black former police chief in Orlando who was vetted by the Biden team for vice president, in a state that has repeatedly proved just out of reach.Ms. Demings raised $4.6 million in her first three weeks, topping Senator Marco Rubio, the Republican incumbent, who raised $4 million over three months. (Ms. Demings spent more than $2.2 million on digital ads raising that sum, records show.)Two other G.O.P. retirements in redder states, Ohio and Missouri, have further destabilized the Republican map, providing at least a modicum of opportunity for Democrats in Trump territory. Republicans face heated primaries in both states.In Ohio, the Republican candidates include the former party chair, Jane Timken; the former state treasurer, Josh Mandel, who has run for Senate before; the best-selling author J.D. Vance; and two business executives, Bernie Moreno and Mike Gibbons.The leading Democrat is Representative Tim Ryan, a moderate who ran briefly for president in 2020, and who entered July with $2.5 million in the bank.In Missouri, the early efforts to woo Mr. Trump have been plentiful, and that includes spending at his Florida resort.Two potential candidates have trekked to Mar-a-Lago for fund-raisers or to meet with the former president, including Representatives Billy Long and Jason Smith. Mr. Long reported spending $28,633.20 at the club, filings show; Mr. Smith, who also attended a colleague’s fund-raiser on Thursday at Mr. Trump’s Bedminster property in New Jersey, according to a person familiar with the matter, paid $4,198.59 to Mar-a-Lago.“I’m expecting someone to start flying over Bedminster with a banner at some point,” said one Republican strategist involved in Senate races, who requested anonymity because, he said half-jokingly, it could end up being one of his candidates buying the banner.Representative Val Demings of Florida is running for the Democratic nomination to challenge Senator Marco Rubio, a Republican.Doug Mills/The New York TimesThe biggest name in Missouri is Eric Greitens, the former governor who resigned after accusations of abuse by a woman with whom he had an extramarital affair. He raised less than $450,000. Among his fund-raisers is Kimberly Guilfoyle, the girlfriend of Donald Trump Jr., and his campaign also made payments to Mar-a-Lago.Three other Republicans in the race out-raised Mr. Greitens: Representative Vicky Hartzler, Attorney General Eric Schmitt and Mark McCloskey, the man best known for waving his gun outside his St. Louis home as protesters marched last year. Some national Republican strategists are worried that if Mr. Greitens survives a crowded primary, he could prove toxic even in a heavily Republican state.Mr. Scott has pledged to remain neutral in party primaries, but Senator Mitch McConnell of Kentucky, the Republican leader, has long preferred promoting candidates he believes can win in November.“The only thing I care about is electability,” Mr. McConnell told Politico this year. With Mr. Scott on the sidelines, a McConnell-aligned super PAC, the Senate Leadership Fund, is expected to do most of the intervening.Mr. Trump, who is often at cross-purposes with Mr. McConnell, has appeared especially engaged in the Arizona and Georgia races, largely because of his own narrow losses there. He has publicly urged the former football player Herschel Walker to run in Georgia — Mr. Walker has not committed to a campaign — and attacked the Republican governor of Arizona, Doug Ducey, even after Mr. Ducey has said he is not running for Senate. Some Republican operatives continue to hope to tug Mr. Ducey into the race.Mr. Trump delivered one early Senate endorsement in North Carolina, to Representative Ted Budd, who raised $953,000, which is less than the $1.25 million that former Gov. Pat McCrory pulled in. Some Republicans see Mr. McCrory as the stronger potential nominee because of his track record of winning statewide. In Alaska, Kelly Tshibaka is running as a pro-Trump primary challenger to Senator Lisa Murkowski, who voted to convict Mr. Trump after his second impeachment. Ms. Murkowski, who has not formally said if she is running again, raised more than double Ms. Tshibaka in the most recent quarter, $1.15 million to $544,000.In Alabama, Mr. Trump gave another early endorsement to Representative Mo Brooks and recently attacked one of his rivals, Katie Britt, who is the former chief of staff of the retiring incumbent, Senator Richard Shelby. Ms. Britt entered the race in June, but she out-raised Mr. Brooks, $2.2 million to $824,000. A third candidate, Lynda Blanchard, is a former Trump-appointed ambassador who has lent her campaign $5 million.Mr. Brooks won over Mr. Trump for being among the earliest and most vocal objectors to Mr. Biden’s victory. The photo splashed across Mr. Brooks’s Senate website is him speaking at the Jan. 6 rally that preceded the riot at the Capitol. In his recent filing, one of Mr. Brooks’s larger expenses was a $25,799 tab at Mar-a-Lago.“The map tilts slightly toward the Democrats just based on the seats that are up,” said Brian Walsh, a Republican strategist who has worked on Senate races. “But the political environment is the big unknown, and the landscape can shift quickly.”Rachel Shorey More