Sometime in January, President Donald Trump received a coronavirus vaccine. Except he didn’t tell anybody. We didn’t find out until March. And while Trump frequently sought credit for the very rapid production of vaccines, he declined to actually urge people to get one until about the same time.

Trump’s reason for this delay was unstated but abundantly clear, as it was throughout his presidency: He was minding his base. It was the same story with masks. It was the same story with plenty of other things that could have lent bipartisan cred to his presidency and might even have saved it, if not for Trump’s laser-focus on catering to his most passionate supporters and not telling them things that might offend their sensibilities.

But now, it’s President Biden’s problem — a big problem that could, thanks in large part to Trump, not just cost the country lives and productivity but also cost Biden his agenda. Conservative vaccine hesitancy will apparently play the biggest role in depriving the United States of herd immunity. Overcoming it is now both significantly more difficult given Trump’s lack of interest in being a forceful messenger, and a problem that his Democratic successor will struggle with because of Trump’s efforts to downplay the virus and mitigation efforts.

Amid a prolonged drop-off in vaccination rates as demand ebbs, the Biden administration has in recent days set about confronting this challenge and applying pressure on those who could assist in the process.

The effort involves, as The Washington Post’s Dan Diamond reported Monday, figuring out how to convince skeptics of both the vaccines’ safety and necessity (the latter of which is probably the most undersold hurdle). It also involves, as The Post’s Isaac Stanley-Becker reported Tuesday, playing a bit of hardball with states, which are responsible for disseminating and administering the vaccine. The Biden administration will no longer distribute the vaccines equitably on a consistent basis, instead giving vaccines that some states decline to order available to other states who might be able to use them.

The move makes sense from a supply-and-demand standpoint. But it also sends a message: If you’re not going to get people to take the vaccine, we’ll send them to states who will.

The latter change comes amid a yawning gap between blue and red states on vaccination rates. The 21 states with the highest percentages of their populations receiving at least one dose? All states Biden won. Fifteen of the 16 states with the lowest first-dose numbers? States Trump won. (The 16th is Georgia, which Biden won but where Republicans are in control of state government.)

The challenge for Biden is particularly acute in our current era. The people he needs to convince to shed their skepticism and get the vaccine are overwhelmingly conservative — exactly the kind of people who are least inclined to listen to him. Many will have concerns about vaccine safety, thanks in no small part to fearmongering by their favored cable-news hosts. But probably more problematic are the ones who simply don’t think it’s necessary. Views of the severity of the pandemic are much more ingrained given they’ve formed over a year-plus, despite now more than half a million deaths.

The most viable argument would seem to involve working around the edges on conservative hesitancy. It’s convincing people not just that the vaccines are safe, but that getting vaccinated will help them return to something approaching normal. It’s convincing them that, even as they personally might face comparatively little jeopardy because they’re relatively young or they don’t have preexisting conditions, that it’s important to protect others they could infect who aren’t so fortunate. It’s warning about variants that could render the vaccines we have less effective and starting the whole process over again. In sum, it’s pitching this as a communal effort to rid us of this problem, making people understand that it’s not just about them personally.

But that’s more difficult for a Democratic president to do. The skepticism is ingrained in large part because Trump fed it, and Republicans are strongly loyal to their defeated president. It was very likely a bad bet on his part, given the continued strain of the pandemic cast a pall over his late presidency. But it doesn’t change where we are today. The effort to “own the libs” when it came to their supposed alarmism about the virus and mitigation plans became something that the GOP itself began to own and will have a difficult time easing away from in the name of urging vaccinations.

We’ve seen little in the way of a concerted GOP effort to move beyond that and get their supporters vaccinated, beyond a few isolated examples such as GOP physicians in Congress cutting a new ad and Trump infrequently now telling people to get vaccinated. There’s been almost nothing in the way of a truly bipartisan and united effort to urge vaccinations.

But the biggest political loser if they don’t, as they probably know, is unlikely to be them. Instead it will be Biden, who is pushing an ambitious expansion of government spending and whose agenda could be held captive if the virus continues to cast a pall over everything else. That’s not to say anybody wants all of this to continue, but people respond to both incentives and to problems that can later be blamed on them specifically.

Because of that, it’s the biggest early test — and perhaps the biggest test, period — of truly how much Biden can turn his presidency into a bipartisan one, as he’s long claimed to want to do. The one thing Biden has going for him is that he doesn’t need GOP votes, but rather for enough of its base to do something more private, that doesn’t necessarily signal support for him personally.

But that doesn’t mean it’s not a steep hill — and a vitally important one to climb for both the country and for Biden’s presidency.