As he was running for president, Joe Biden was pointed in arguing for one necessary response to the existing political environment in America: Democrats and Republicans had to be willing to work together.

This call for unity was in part an obvious response to his opponent, President Donald Trump.

“Everybody knows who Donald Trump is,” Biden said at a rally in Michigan in October, for example. “Let’s keep showing them who we are. We choose hope over fear. We choose unity over division.”

But it also is a belief he has articulated often, one that has been a part of Biden’s politics since well before he was tapped to serve as Barack Obama’s vice president. So at his inauguration, the same message: unity.

“To restore the soul and secure the future of America requires so much more than words,” he said in his inaugural address. “It requires the most elusive of all things in a democracy: unity.”

In the days after he was inaugurated, Biden’s critics seized upon his calls for unity as a way to bash him for enacting policies he had promised on the campaign trail or for deciding not to continue policies implemented by Trump. Pulling back Trump’s highly divisive ban on travel from many Muslim-majority countries was cast as undermining Biden’s pledge to unite the country by none other than former Trump adviser Stephen Miller, neatly encapsulating how the call for unity could be exploited for bad-faith rhetoric.

That, of course, is the problem with calls for unity: You can’t unify all by yourself. Unity either demands compromise or necessitates complete surrender. As his team explained to The Washington Post during the campaign, Biden hopes that addressing the problems plaguing the country will force unity from the bottom up. But that will often mean passing legislation, and if congressional Republicans learned any political lesson from the Obama administration, it’s that resisting a Democratic president’s initiatives can lead to a sense that change is needed — and then lead to Republican control of the House and the Senate.

Speaking to reporters on Monday, Biden may have made things a bit harder for himself still. An administration that has been very careful about managing expectations just established a high bar for working with its opponents.

Asked by The Post’s Annie Linskey how he would measure success at unifying the country, Biden first suggested that a reduction in the omnipresent nastiness in politics would be one standard.

Then he set another.

“Unity also is trying to reflect what the majority of the American people — Democrat, Republican, independent — think is within the fulcrum of what needs to be done to make their lives and the lives of Americans better,” he said. He pointed to polling showing that most Americans, regardless of party, think the government should act to address the economic damage from the coronavirus pandemic.

“Unity also is trying to get at, at a minimum — if you pass a piece of legislation that breaks down on party lines but it gets passed, it doesn’t mean there wasn’t unity. It just means it wasn’t bipartisan,” he later added. “I prefer these things to be bipartisan because I’m trying to generate some consensus and take some of the vitriol out of all this.”

The latter measure very much depends on a good-faith response from his political opponents. It requires Republicans being willing to not vote in lockstep on policy issues.

But the first measure may be trickier. If the bar is majority support for a policy — in his example, he stated that about 3 in 5 Americans supported his proposal — that opens Biden up to a range of attacks elevating policies he opposes as necessary for “unity.”

For example, polling conducted by Marist University for a Catholic organization last January found that most Americans support tighter restrictions on the availability of abortion than Democratic elected officials have supported in the past. By elevating similar data on other issues, Republicans can claim that Biden isn’t upholding his own assertion that unity demands respecting the will of the majority. Republican legislators could similarly rationalize opposing legislation on the basis that it lacks majority support in polling or has only plurality support.

Biden was careful to note that polling isn’t perfect, but that opens another problematic door. There are a lot of pollsters out there of varying reliability. There’s nothing to stop commentators from elevating dubious polls as a rationale for mandating action by Biden or for opposing efforts he wants to undertake. It’s easy to predict a moment when Biden advocates a policy that has 57 percent support (which he said his coronavirus package enjoyed) only to see his opponents lift up a Breitbart-sponsored poll that shows 60 percent in opposition. The playing field shifts from advocating policies central to his politics to tiresome debates about which polls best capture what Americans want to see and how that does or doesn’t respect calls for “unity.”

The president’s point is obvious: He thinks Congress and the government should work toward the things Americans want to see happen. But such directness and simplicity is simply grist for politics as usual at the moment. You have to scale back toxicity before you can assume that your political opponents will act in good faith, not rely on their good faith to tamp down on toxicity.

There’s a quote from Biden that gains new resonance with each passing day. Shortly before the 2012 election, in which he earned a second term as Obama’s vice president, Biden offered a prediction: Obama would win and politics would change.

“We need leaders that can control their party,” he said of the GOP’s opposition to Obama’s administration, “and I think you’re going to see the fever break.”

That did not happen then, and it’s not clear why it might now.