Former Vice President Joe Biden likely selected Sen. Kamala Harris for his running mate so he could try and present himself as tough on crime. After all, Harris is a former prosecutor who relentlessly went after relatively minor offenders during her tenure.

Further, Biden had long enjoyed good relationships with the nation’s police unions. After all, they backed him and Barack Obama during both their campaigns for president.

However, that was then and this is now.

Today, we live in a world where legions of leftist want to defund law enforcement to varying degrees. Acting too pro-law enforcement isn’t going to please the base very much, though that’s the same base that will likely vote against President Trump anyway. Regardless, some still want to try and paint the Biden ticket as pro-police.

It ain’t working.

Bill Johnson knew, before he reached out to Joseph R. Biden Jr.’s campaign last spring, that things had changed between the former vice president and the nation’s police unions. A once-close alliance had frayed amid clashes over police brutality and racism in the justice system. Still, Mr. Johnson, the executive director of the National Association of Police Organizations, invited Mr. Biden to address the group as it weighed its 2020 endorsement.

For weeks, the campaign was politely noncommittal, Mr. Johnson said. Finally, he recalled, on the day NAPO was deciding its endorsement, he heard from a campaign aide asking if there was still time to send a message. “Not to be a jerk, but we were literally starting the meeting,” Mr. Johnson said. “It’s kind of a little late.”

The police federation, which twice endorsed the Obama-Biden ticket and stayed neutral in 2016, backed President Trump in July. Soon after, its president told the Republican convention that Mr. Biden and Senator Kamala Harris were “the most radical anti-police ticket in history.”

That attack marked a low point in a political relationship that had endured for most of Mr. Biden’s career.

If elected, Mr. Biden would bring to the White House a long career’s worth of relationships with police chiefs, union leaders and policy experts that is unmatched by any other major figure in the Democratic Party, according to more than a dozen current and former law-enforcement officials who have worked with Mr. Biden in various capacities.

During a late-summer speech in Pittsburgh, Mr. Biden pledged to draw both racial-justice activists and police leaders “to the table” to forge durable solutions.

“I have worked with police in this country for many years,” Mr. Biden said. “I know most cops are good, decent people. I know how they risk their lives every time they put that shield on.”

Yet the 2020 election has also underscored the difficulty Mr. Biden may have in achieving that goal. He is presenting himself as both a criminal-justice reformer and a friend to diligent police officers, a critic of racism and rioting alike.

In short, Biden is trying to walk the line between appeasing the voter base and appeasing people like police unions, and it’s simply not working. These are two diametrically opposed groups that are at odds in ways that aren’t going to be hammered out before the election. Biden is trying to walk a tightrope during an earthquake.

It’s just not going to happen.

Yet let’s also take a look at Biden’s police support in the past. Note what’s missing from the list of “police chiefs, union leaders and policy experts” listed? That’s right, actual street police.

See, police chiefs are political animals, especially in larger cities. They reflect the policies and politics of the elected officials they answer to, not the police who are involved in the nitty gritty of day-to-day police work. Oh, in smaller communities, it can be different, but presidential candidates don’t care about support from the chief of the Leary, GA police department, they care about the chiefs in Chicago and New York. Those are the ones that let them paint themselves as pro-police.

Yet sometimes, these chiefs aren’t even pro-police. Not really.

It doesn’t matter, though, because Biden’s not getting their support this time around. While they’re not backing Trump necessarily, they’re not backing Joe either, and that’s got to sting.

Then again, you can’t offer support for anti-police rioting until the polls show it’s unpopular and still think the police are going to like you. As a result, all that past support that some Biden supporters like to tout? It means jack squat.