LOWRY/Who says bipartisan cooperation is dead?

Joe Biden and Donald Trump are proving that even sworn enemies can cooperate to promote one another’s political interests.

President Biden, with his criticism, and his Department of Justice, with its search of Mar-a-lago and related investigation, have boosted Trump’s profile to the benefit of both Biden and his party and of Donald Trump.

Everyone wins, except Republicans increasingly worried about the midterms and anyone hoping that the GOP would turn the page in 2024.

Several weeks ago, Republicans were nervous that Trump would announce his latest presidential bid prior to the midterms. Now, it is almost irrelevant — Democrats and the DOJ have effectively announced for him.

Whenever things aren’t going well for a White House or a political campaign, the natural advice is to try to change the subject. This often doesn’t work — the maneuver is too obvious, or the new hoped-for subject can’t possibly compete with the old unwelcome subject.

That’s not the case here. Trump is something everyone wants to talk about: people who love him, people who hate him, journalists whose work gets more clicks and viewership, and of course, above all, Trump himself, who has never found any other topic quite as compelling or important.

To the extent Republican officials and candidates identify themselves with Trump’s delusions about 2020 and get sucked into debating whether the FBI should exist, they are creating vulnerabilities or distractions where none need exist.

According to a new CBS News poll, 47% of voters say that how they feel about Trump will have “a lot” of influence on how they vote. Independents who say that Trump is a factor for them are voting to oppose him by a 4-1 margin.

All of this is good for Democrats in general and Biden in particular. If the president can define himself as the last, best obstacle to Trump returning to the White House, it helps quell the extensive doubts about him within his own party. Biden is barely above 40% approval in polling averages, a nightmarish position, and yet he’s only down 2.2% in a hypothetical rematch with Trump in 2024, according to RealClearPolitics.

Trump is his life-preserver and comfort blanket, providing a political boost based on the easiest political argument in the world — “See that guy over there obsessed with fanciful theories about the 2020 election? I may not be a very good president. But at least I’m not him.”

Meanwhile, the Trump phenomenon has always been a form of political jujitsu, using the force deployed against it as a source of strength. The more Trump is called names and investigated, the better. Not to make light of it, but if the FBI had shown up at Mar-a-lago with an armored vehicle and a couple of helicopters, Trump’s lead over Florida Gov. Ron DeSantis, which had dwindled before jumping back up after the search, would be all but insurmountable.

If Trump is bolstered by Biden’s hostility, he also benefits from his weakness. Trump’s favorable rating is about 40%, a poor showing that would be enough to make him the underdog against any president who hadn’t been cratering over the past year. Trump doesn’t just narrowly beat Biden in prospective 2024 polling, he handily defeats Vice President Kamala Harris. There’s being fortunate in your enemies, then there’s hitting the jackpot.

So Trump and Biden compensate for one another’s weaknesses, and they are effectively working together to get Trump nominated — which Trump wants because it’s the first step back to the White House and Biden wants because Trump would be the riskiest GOP candidate in a general election.

It’s not the most edifying relationship. Indeed, it’s a de facto partnership toward a demoralizing re-run of 2020. But neither Trump nor Biden is as likely to get where they want to go without the other.

Rich Lowery is editor of National Review, ­a leading conservative magazine founded by William F. Buckley.