There are as many reasons to impeach or not impeach President Trump as there are House Democrats. As The Post’s Mike DeBonis, Rachael Bade and Paul Kane reveal in talks with 45 lawmakers, whether to support an impeachment inquiry is a deeply personal decision that doesn’t necessarily align with a lawmaker’s politics.

One of the most salient arguments I’ve heard for impeachment from legal experts is one I’ve started to hear from lawmakers, too: What will the history books say?

Here's how it goes:

Most Democratic lawmakers in the House seem to think the president of the United States obstructed an independent investigation, lied to the American people and maybe even broke the law, all while refusing to cooperate with Congress. House Speaker Nancy Pelosi (D-Calif.) has even used the term “constitutional crisis” to describe the moment Congress is in right now.

Given all that, how will they explain to future generations why they didn’t open impeachment proceedings regarding the president? Because they were worried about the next election? Will that argument hold water a decade or more from now?

“There’s going to come a day when we all have to answer for what we did in this moment,” said Rep. Daniel Kildee (D-Mich.) in explaining his support for an impeachment inquiry despite the fact he represents a district Trump nearly won in 2016.

The power of this history-book argument lies in how narrow it makes the anti-impeachers’ concerns appear. Democrats who don’t want to impeach Trump are worried it could cost them the 2020 House majority, or the White House, or both. But that’s one election. Impeachment is a mark that will last forever. It’s Congress telling future Congresses and future presidents, that Trump’s behavior as outlined in the Mueller report is not okay.

It’s symbolic, yes, but impeachment represents symbolism that will stand the test of time. Only two other presidents have been impeached by the House — Andrew Johnson and Bill Clinton. A third, Richard Nixon, resigned before proceedings began. Those names are boldfaced in the history books, while other transgressions by past presidents have faded into the background.

“One hundred years from now, no one’s going to remember what speech Pelosi is going to give about Trump’s behavior,” said Jens David Ohlin, a vice dean at Cornell Law School and one of the more eloquent expounders of the history-book argument I’ve talked to. “But historians are certainly going to remember that Trump is going to be impeached by the House.”

A common counterpoint from the anti-impeachers is that impeachment by the House won’t get Trump out of office. The Republican-controlled Senate does not have the votes to convict him — the last step required to oust a president.

But the history-books argument has a powerful rebuttal to that, too: It’s less important for Trump to be removed from office than for Congress to be seen attempting to rebuke him for his behavior.

History, Ohlin continued, will remember that “there was a contentious debate in the Senate during an impeachment trial where his lawyers were forced to defend his conduct. Historians will remember that, and it will be a black mark on his record.”

There would be an asterisk next to Trump’s name, well, forever. And that counts for something. Behind closed doors, even Republicans will say they don’t approve of Trump’s behavior on any number of issues, especially as outlined in the Mueller report. One Republican, Rep. Justin Amash (R-Mich.), is saying that publicly.

Of course, there are some lawmakers who look at their impeachment decision through the lens of the history books and come to the opposite conclusion: that they’ll be blamed for creating a divisive political environment, as House Republicans often are in accounts of Clinton’s impeachment in 1998-'99.

"That’s not healthy for my little 3-year-old grandson,” Rep. Emanuel Cleaver II (D-Mo.) told The Post. “I would like to be able to say that I stood for maintaining the unity of the country.”

Layered in that argument is the fact that public opinion does not favor impeachment. Polls show that a majority of Americans oppose it, even if most think Trump lied. The most recent, a June 2 CNN poll, finds 54 percent of Americans are against such a step, with 41 percent for it. Impeachment is a political act, and just as Congress probably wouldn’t try to pass a law that’s unpopular with the country, why would it impeach a president when the country doesn’t support it?

But public opinion today is a very different measure from public opinion years from now. It’s also arguably irrelevant to how America eventually remembers this moment. Sometimes the morally right thing is not the most popular thing to do.

One reason public opinion may not be on Congress's side is because Congress itself isn't very popular. Impeaching Trump would be an act of Congress asserting its power over the president. As Trump has blocked 20 congressional investigations into him or his administration, Congress's need to assert its authority to oversee the executive branch gets more and more urgent.

Today, the legislature’s very reputation as a coequal branch of government is at risk, argues this camp. Kerry Kircher, a former counsel for the House, put it this way to The Fix recently: “Can Congress, without picking up the cudgels and investigating the president . . . continue to function as a serious independent branch of government if it does not do that? I think not.”

Special counsel Robert S. Mueller III has appeared to put the onus on Congress to act. “The Constitution requires a process other than the criminal justice system to formally accuse a sitting president of wrongdoing,” he said in a rare news conference last month.

The debate over whether to impeach transcends politics. Lose your job? Lose the majority in the House? Lose the White House? Those are all risks that impeachment could exacerbate — or maybe even things it could cause. (Or maybe the conventional wisdom is off.)

But this is one election. History books are forever. And that’s why this pro-impeachment argument is one of the most arresting I’ve heard. Watch for more lawmakers to make it to get a sense of whether House Democrats are indeed going to open impeachment proceedings against this president.