In many ways Joe Biden will enter the presidency in a politically enviable position. The arrival of the coronavirus vaccine means that, after running as the candidate of normalcy, he is poised to preside over its literal return, which could include not just economic recovery but also a period of personal exuberance — at last, restaurants! amusement parks! vacations! — that will feel much more euphoric than the post-financial-crisis grind did under Barack Obama 12 years ago.

At the same time, the fact that Biden did not lead his party to a landslide will also give him certain political advantages. He will not be permitted to re-enact the New Deal or the Great Society, but neither will he be tempted into ideologically driven debacles like Bill Clinton’s failed health care push or even Donald Trump’s failed attempt to repeal Obamacare. Having Joe Manchin and Susan Collins as the most powerful figures in the Senate will not be good for progressivism’s policy objectives, but it could be very good for Biden’s popularity, enabling him to chart a moderate course while telling the left, sorry, but my hands are tied.

In the best-case scenario for Biden, the Trumpian voter-fraud narrative could set in motion a Tea Party redux on the right, with fringe characters and Trump loyalists successfully primarying established G.O.P. figures — but without the high-unemployment economy and the Obamacare fight that enabled the Tea Party Republicans to take the House in 2010. Instead, a radicalized Republican Party campaigning on a supposedly stolen election while the Democrats campaign on prosperity and normalcy could set up the rare midterm scenario in which an incumbent president’s party actually picks up seats.

If you want to know how the Biden administration could blow this opportunity, though, look no further than his just-announced choice to run the Department of Health and Human Services, Xavier Becerra.

No cabinet agency is likely to be as prominent as H.H.S. during the first year of the Biden presidency, given the upcoming vaccine rollout and the slow unwinding of public-health restrictions. And for a campaign that placed so much emphasis on the idea that disinterested expertise and capital-S Science should guide the coronavirus response, Becerra is a peculiar choice: a partisan politician from a deep-blue state whose health care experience is mostly in legal battles with the Trump White House over Obamacare, rather than in health policy or medicine itself.

Of course cabinet secretaries are often party hacks, but even Trump chose a physician and then a pharmaceutical executive for the H.H.S. post, and it’s especially odd — as the Times story on the selection notes — to pick a partisan at a moment when so many medical groups were urging the Biden administration to elevate doctors and other acknowledged experts to lead pandemic-era policy.

It’s less odd, though, if you anticipate using your cabinet agencies the way the Obama White House did in its otherwise-gridlocked second term — as aggressive instruments of partisan policymaking, especially on culture-war issues where Congress is particularly loath to act.

Under Obama, this strategy encompassed everything from his attempted immigration amnesties and gun-control executive orders to his Education Department’s interventions in college sexual-assault policies and school-bathroom regulations to the long-running attempt by H.H.S. to force religious employers like the Little Sisters of the Poor to cover contraception and morning-after drugs.

It was inevitable that a Biden administration would pick up some of these threads. But Becerra is the pick you make if you intend to pursue a lot of them, since that’s where his qualifications lie — as a partisan warrior on issues like guns and immigration and as an abortion-rights maximalist who has used his attorney general’s office to sue the Little Sisters of the Poor after a Supreme Court decision in their favor and to pursue felony convictions against the pro-life filmmakers who made undercover videos of Planned Parenthood executives talking about the sale of fetal body parts. (That prosecutorial push was denounced for “disturbing overreach” by the Los Angeles Times editorial page, which is not exactly noted for its pro-life sympathies.)

As John McCormack of National Review puts it, to understand how social conservatives feel about Becerra, imagine if a Republican president elected on a promise to heal partisan wounds and deal with a pandemic nominated Rick Santorum as his first secretary of Health and Human Services.

Now most Americans aren’t social conservatives, and Becerra will have media and Democratic establishment support in many of the fights he might pick. But Biden won the presidency in part because he was more popular than his party (to say nothing of the press), and deploying his bureaucracy aggressively for liberal ends would be the easiest way for him to squander some of that advantage.

Especially since America doesn’t have a conservative coalition these days so much as it has an anti-liberal one, with different groups united by their anxieties about different aspects of a consolidated progressive agenda. That means that liberals can be deceived by polls even when they’re accurate, because they seem to show that on issue X or Y or Z, the liberal position is popular — while eliding the fact that the full spectrum of liberal policies activates intense anxiety and opposition in multiple different highly motivated groups.

A Democratic presidency that genuinely tried to address some of those fears, at a time when the economy is recovering and the G.O.P. could be going Trumpishly insane, might consolidate and expand the victory that Biden just won. But a Becerra-fied Democratic presidency, in which the bureaucracy is using “public health” as an excuse to battle gun owners one week and Catholic hospitals the next, will be successful only in keeping the conservative coalition united, loyal and activated.

One of Biden’s greatest strengths as a politician in a polarized era is that he remembers a time when an ideological liberalism led Democrats into sweeping electoral defeats. Becerra, like Kamala Harris, has a very different background: He comes from California, a state where demographics and a hapless opposition have delivered the Democrats a near-permanent majority — meaning that their leaders have few incentives to compromise with or reassure right-leaning voters, and little experience even attempting that feat.

The tension between those two experiences, and the political attitudes they forge, was always destined to run through a Biden administration. But Becerra’s nomination is an early sign of how the conciliation that succeeded for Biden on the campaign trail might be abandoned, and a great political opportunity thrown away.

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