Until Tuesday’s exhausting opening day of Senate removal hearings, Senate minority leader Chuck Schumer had been keeping an uncharacteristically low profile. Normally, no one in American politics is quicker to make a beeline towards the nearest TV camera. But on impeachment he has deferred to House Speaker Nancy Pelosi and her crew of eager anti-Trump fighters like Representative Adam Schiff. Compared to the zealous arguments made by Pelosi on the necessity of impeachment, Schumer has been quieter and more cautious.

Now that impeachment has moved to the Senate, Schumer can’t avoid taking a stand. It’s clear that he is not eager to relitigate the arguments for impeachment, a redundant action in any case, since they’ve been made in the House. Instead, he is focusing his energy on fighting for procedural fairness in the Senate trial.

On Tuesday, Schumer pushed back against Senate majority leader Mitch McConnell’s attempt to engineer a speedy trial. Schumer won a few narrow victories, thanks to moderate Republicans who agreed with some of the complaints by Democrats that McConnell was ramming through a farcical non-trial, run on a marathon schedule and without admitting the findings of the House impeachment inquiry. Thanks to these moderate Republicans—led by Susan Collins, Rob Portman, and Lisa Murkowski—the Democrats were able to fend off the most extreme of McConnell’s tactics.

It’s exactly those moderate Republicans Schumer is making his pitch to with the amendments he’s introduced (11 so far) to subpoena witnesses and documents. But on the issue of witnesses, none of the moderate Republicans proved amenable. All the amendments died by a strict party-line vote of 53-47.

Introducing the first of his amendments, Schumer said, “We feel this is an obligation we have to the Constitution, to outline what a fair trial would be, to not go along with a cover-up, with a sham trial. And we will do it. We will do it. Right off the bat, Republican senators will face a choice about getting the facts or joining Leader McConnell and President Trump in trying to cover them up. This is a historic moment. The eyes of America are watching. Republican senators must rise to the occasion.”

Schumer’s agenda, then, is a narrow one. He wants a “fair trial” and he threatens Republicans with being tarred as complicit in covering up Trump’s crimes if they don’t provide one. This emphasis on procedural fairness could be dismissed as weak-tea politics. It turns impeachment into a question about Senate rules rather than Trump’s crimes. A true swing-for-the-fences strategy would aim for Trump’s removal.

But Schumer’s strategy is dictated by his position. Unlike Nancy Pelosi in the House, Schumer is in a minority in the Senate. He has 47 Democratic and independent votes against McConnell’s 53 Republicans. Further, removal would require a 67-vote supermajority, a near impossibility in this era of GOP hyper-partisanship, when the GOP might well remain loyal even if Trump actually shot someone on Fifth Avenue and then returned Alaska to Russian control.

Moreover, focusing on the procedural fairness of the trial is, if polling is to be trusted, a way of getting the vast majority of Americans on your side. A CNN poll found that impeachment has majority approval (51 percent support as against 45 opposed). But, more significantly, an overwhelming majority (69 percent) said the Senate trial should hear testimony from new witnesses. Even more rank-and-file Republicans support calling new witnesses (48 percent) than oppose it (44 percent).

If we consider some of the moderate Republicans facing reelection, the majority is even larger. Colorado, where Republican Senator Cory Gardner is up for reelection, supports impeachment by 56 percent to 41 percent. In Maine, Susan Collins will face an electorate that supports impeachment by 61 percent to 37 percent.

Schumer’s gamble is that these voters will care enough about procedural fairness that they will punish senators who voted against calling witnesses. The Republicans are operating from a different theory of the electorate. The GOP assumption seems to be that partisan polarization drives more people than concern about procedural fairness, so at the end of the day the best option is to appeal to the loyalty of Trump voters who feel he is being treated unfairly. That was the burden of the argument of Republican lawyers who defended the president on the Senate floor. They repeatedly echoed the right-wing narrative that Trump is an innocent president targeted by Democrats seeking to overturn the 2016 election.

Schumer’s argument is a dispassionate one made to the broad public, including many Republicans who might be uneasy about Trump even if they oppose impeachment. The Republican pitch is all about stirring up primal fears among the Republican base.

Holding a weak hand, Schumer has acquitted himself well. One possible objection to his strategy is the contradiction between trying to win over Senate Republicans and also bludgeoning them with the threat that they’ll be held complicit in a cover-up.

On Twitter, Mitch McConnell’s former campaign manager Josh Holmes gloated, “Schumer always takes the bait. Wearing senators out on meaningless process votes day 1 when his entire strategy relies upon bipartisan consent for a drawn out process. The mood in the chamber will be toxic by Saturday.”

Susan Glasser of The New Yorker thought Holmes might have a point. “Is Schumer needlessly alienating possible votes?” She asked. “Those senators looked pretty miserable pretty quickly in the chamber.”

But of course, there are different ways to read that misery. It could be that they looked depressed not just because they were mad at Schumer but also because they knew he had caught them in a trap. They were being forced to align themselves with Trump in way that will prove lethal in November.

If that trap does spring the way Schumer set it to, moderate Republicans who stick with Trump will go down to defeat. Schumer’s bet on impeachment fairness could yet prove to be a political masterstroke.