Most Republicans don’t spend a lot of time defending President Trump’s actions as he faces impeachment in the House. That he spoke with Ukrainian President Volodymyr Zelensky in July and asked for investigations that would benefit him personally, that this was part of a broad effort to get Ukraine to announce similar investigations — these are generally uncontested points. Instead, Republicans have focused heavily on criticizing the impeachment effort as politically biased, a partisan move by Democrats intent on impeaching Trump since the very first days of his presidency.

Both can be true, of course: Democrats could have wanted to see Trump ousted from the get-go, and they also could have identified Trump’s interactions with Ukraine as a particularly noxious act that demanded he be removed from his position. But what that Republican argument obscures is the extent to which partisanship is playing to Trump’s benefit, not his disadvantage.

There has been a great deal of attention paid in recent weeks to the idea that impeachment should be a bipartisan affair, an act that reaches across the aisle to find broad support. The thing about bipartisanship, though, is that it requires two actors. That’s what the prefix means, as any middle school English teacher can attest. So if one party simply refuses to work in a bipartisan fashion, bipartisanship is impossible.

Who is the obstinate party on impeachment? Republicans claim it’s the Democrats, for not engaging in a process which the Republicans felt was fair. As the impeachment inquiry proceeded, Democrats addressed various stated concerns expressed by their opponents (the need for open hearings, the need for a vote, requests for some witnesses) while not opening the door wide enough for Republicans to derail the process. Often, those changes were met with a fruit-of-the-poisonous-tree response: Since Democrats didn’t acquiesce to Republican requests from the outset, nothing that followed was valid. At times, this argument extended back to the August complaint from an intelligence community whistleblower.

By way of demonstrating how the current process differs from the last impeachment, that of President Bill Clinton in 1998, Trump allies point to the fact that several Democrats joined with Republicans in supporting the articles of impeachment that passed the House. We can visualize that support by looking at the vote on Article I, which accused Clinton of perjury. It passed, 228-206 (including the “no” vote of then-Rep. Bernie Sanders (I-Vt.)). (Ideological views below are calculated by Voteview and positioned to favor visual density.)

The cross-partisanship is modest. Five Democrats supported impeaching Clinton, and five Republicans opposed it. (Those votes included two sitting members of the House, Reps. Collin C. Peterson (D-Minn.), who supported it, and Peter T. King (R-N.Y.), who didn’t.)

Notice, though, how the center of that graph, the ideological middle, houses a number of representatives. That’s different from how things look today, something we reported last week when we similarly visualized the House Judiciary Committee votes that authorized articles of impeachment for Trump, Clinton and, in 1974, Richard M. Nixon.

On that committee, there wasn’t much overlap between the two sides. Certainly less than was the case under Nixon. But the shift to the right among members of that committee since 1998 is particularly obvious, especially compared with the committee’s Democrats.

What’s shown above are the Judiciary Committee votes in which there were the most defections from members of the president’s party. In 1998, there was precisely one defection in the committee across the four proposed articles: A “no” vote by now-Sen. Lindsey O. Graham (R-S.C.).

That article ended up being rejected by the full House. That vote was closer than the abuse of power charge Clinton faced, Article IV. In this vote, you can see the importance of ideological moderation: There are a lot more defections among the Republicans who were more moderate than the party average. Four out of five defections were among more moderate Republicans; 86 percent of those more conservative than average voted to impeach Clinton on that count.

That dynamic is what resulted from a less polarized Congress. The Oct. 31 vote formalizing the impeachment inquiry saw only two defections, one from Peterson and one from Rep. Jeff Van Drew (D-N.J.), who reportedly plans to switch parties. Every other vote was on party lines, with no representatives caught in any tug-of-war in the middle.

Van Drew’s anticipated switch has been isolated by critics of impeachment as evidence that even some Democrats find it hard to stick with the partisan push they’re seeing. That ignores two factors, though. The first is that Van Drew’s decision is certainly complicated by the fact that Democrats in his district really want him to vote to impeach, potentially affecting a Democratic primary.

The other is that Van Drew would be the second member of Congress to change parties this year in response to Trump. The other is Rep. Justin Amash, who in July announced he was leaving the GOP after repeatedly criticizing the party’s response to the report completed by former special counsel Robert S. Mueller III. Amash became an independent, but the idea is the one articulated above: There was no place for someone who supported impeaching Trump in the Republican Party. Amash’s situation is different from Van Drew’s in an important way, though. His district, like Van Drew’s, leans Republican, and there’s no sign that his decision was motivated by polling.

Amash is one of the more moderate Republicans, though not as moderate as Peterson. When Amash was a member of the current Republican caucus, he would have been in the fifth percentile, according to Voteview’s calculus (which admittedly doesn’t capture the complexity of Amash’s positions). Were he in the 1998 Congress, though, he would have been in the 20th percentile of a more moderate caucus.

The Democratic caucus hasn’t gotten significantly more partisan since then. About 53 percent of current House Democrats are more liberal than the 1998 caucus average — or about half. Seventy-four percent of the current Republican caucus is more conservative than the 1998 caucus average for that party.

Put simply, the current impeachment fight is happening at a moment when Republicans are quite a bit more conservative than they were during the 1998 fight. They’ve receded from the middle — in part because of losses in 2018, which gave the Democrats the majority they are now using to execute the impeachment inquiry.

But there’s an even more telling factor here that suggests it’s Republican partisanship that is siloing views of impeachment: polling.

In December 1998, with the Clinton impeachment looming, The Post and our polling partners at ABC News asked Americans whether they supported impeaching the president. About a third did, including a bit under 6 in 10 Republicans and 13 percent of Democrats.

In a poll released by Fox News on Sunday, support for impeaching Trump topped 50 percent — including 90 percent of Democrats and about 14 percent of Republicans. In other words, support from within the president’s party was about the same — but support for impeachment from the opposition and from independents is significantly higher than it was then.

The Fox poll found that 11 percent of those who had voted for Trump in 2016 support impeaching him now.

So where’s that represented in the current Republican positions in the House?

No Republicans have indicated that they plan to vote to impeach Trump. Ex-Republican Amash says he will; the two Democrats who opposed the inquiry have said they will oppose it. No Republicans have yet indicated they’ll support impeachment; only one is even a question mark. Despite impeachment having the support of about half of independents and 1 in 10 Republicans, Republicans in the House — all of whom represent Republican-leaning districts — are so far unanimous in opposition. Nine of them supported impeaching Clinton on the article of impeachment that failed by the widest margin when there was 32 percent support for impeaching him.

Notice, also, the dynamics of reporting how members plan to vote. There are regular updates on how more-moderate Democrats plan to vote, but less so among the smaller pool of Republicans. Part of this, it’s safe to assume, is a function of having a general understanding of how they plan to vote.

One can draw whatever lines one wishes to demonstrate that one party or the other is preventing the House from working across the aisle. But it defies credulity to suggest that the problem lies entirely with the Democrats and not, to some significant extent, a GOP that has moved to the right and that shows no indication of allowing dissent within its caucus.

The result? Republican partisan unity has the ironic effect of letting the party argue that it’s the Democrats who are relying on partisanship, while ensuring that the impeachment vote is as close as it can be. Trump is benefiting from partisanship more than he’s hurting from it.