Even before the second impeachment trial of Donald Trump began this week, the outcome was generally understood: Once again, he will almost certainly not be convicted, with the overwhelming majority of Republican senators choosing to acquit him on the charge passed by the House.

The math is fairly simple in the abstract. Conviction requires a two-thirds majority of the Senate to agree — 67 votes — meaning that 17 of the 50 Republican senators would need to agree with the charge offered in the House’s article of impeachment. That article passed the House on a historically bipartisan vote, with 10 Republicans joining the Democratic majority in supporting it. But that’s only about 5 percent of the party caucus in the House, the equivalent of two Republican senators joining the Democrats in the Senate vote. Two, as you’re probably aware, is fewer than 17.

The odds are good that more than two Republicans will vote to convict Trump when the trial concludes. But there are a lot of reasons to think that the total votes to convict will fall well short of the necessary two-thirds.

Consider the composition of the Republican caucus in the Senate. There are only three sitting GOP senators from states that Trump lost in 2020 and only nine others from states where Trump’s margin of victory was less than 10 points.

As that image shows, many Republican senators are not up for reelection until 2024 or 2026, providing a buffer from political blowback for their votes. Sixteen Republicans will face voters in 21 months (four other Republicans have announced that they don’t plan to seek reelection).

There are a few ways to consider that group of senators. Those not seeking reelection might be understood to be freed up to vote their consciences on the issue — as Senate Minority Leader Mitch McConnell (R-Ky.) has repeatedly cleared them to do. Those hoping to serve another six years may be more likely to reflect the concerns of their states’ voters: Those from bluer or blue states may be more prone to vote to condemn Trump, while those from red states may be less inclined to do so.

Except, of course, that many of those Republicans up for reelection next year will face off against potential primary challengers, other Republicans seeking their party’s nomination from a primary electorate that historically tends to be more partisan.

How do Republican voters view Trump’s impeachment? As was the case in the 2020 trial, the vast majority oppose voting to convict the former president, as we reported earlier this week.

A new CBS News-YouGov poll released on Tuesday gets more to the point: Republicans who vote with their conscience against Trump would be seen by 7 in 10 Republican voters as disloyal to the party.

It’s easy to imagine, then, a Republican senator from a purple state who chooses to convict Trump facing a more partisan primary opponent who casts the vote in precisely that light. And it’s easy to see that challenger winning.

In fact, The Washington Post’s compilation of which Republican senators might vote to convict Trump shows a disparity of when senators are up for reelection and of how pro-Trump their states were last year.

We are under no illusion that all of those senators will vote to convict, although it seems likely that several will. Sen. Mitt Romney (R-Utah) did so last year, after all. Idaho’s two senators, Mike Crapo and James E. Risch, represent a state Trump won by 30 points; their openness to conviction is probably not going to culminate in a vote to convict.

Of course, it can be tricky to predict such things. Those 10 House Republicans who voted to impeach Trump in January themselves represented a diverse political range of districts. Rep. Liz Cheney (R-Wyo.) represents one of the most pro-Trump states in the country but voted to impeach. Perhaps Risch and Crapo will take a similarly conscientious stand.

Even if they do, it wouldn’t tip the scales. You’ve probably already counted the dots on the above graph. Twelve Republican senators are identified as open to conviction — five short of the 17 needed to convict. Maybe others will be lured to that cause over the course of the trial, but initial indicators don’t suggest they will. Most Republican senators, including Risch and Crapo, voted to block the trial itself on the grounds that it was unconstitutional, suggesting a low likelihood that they would then take a firm stand against Trump once the trial concludes.

The House Democrats presenting the case against Trump understand that the odds are against them. The case they’re making is ostensibly focused on the senators but is more broadly an effort to convince the public that Trump should be found guilty. After all, if the public, including Trump’s base of support, is convinced that his actions were improper, it may be the best chance Democrats have to flip more Republican votes.

One would be forgiven for assuming that the probability of this happening is low.