Impeachment is entangled in politics in numerous ways. The Senate trial of Trump is taking place in an election year, when Trump, the House of Representatives, and a significant chunk of the Senate will face the electorate. The Democratic primaries are in full swing, and the senators running for president, notably Elizabeth Warren and Bernie Sanders, will have to juggle attending the trial with campaigning.

Democrats, out of an understandable desire not to be seen as carrying out a vindictive partisan grudge, have talked about impeachment as a grave duty. Tweeting about the first day of Senate trial, Connecticut Senator Chris Murphy observed, “The vibe in the Senate was fundamentally different than any other day in the Senate. Totally somber. You could hear a pin drop when the House managers walked into the chamber. I sit next to @SenWarren and we agreed that our overwhelming emotion was sadness.”

Republicans, by contrast, played up the political theater of the event. Lindsey Graham, perhaps Donald Trump’s leading defender in the Senate, warned that the Senate trial was becoming a “complete circus.” Arizona Senator Martha McSally engineered a theatrical photo-op by picking a fight with CNN reporter Manu Raju. The reporter asked McSally if she would consider new evidence for the impeachment trial. McSally lashed out, saying, “You’re a liberal hack I’m not talking to you.” She later went on Fox to gloat about the clash, which she’s using to goose her fundraising.

Graham and McSally are cynically debasing the political process. But there is a more responsible way to take the political dimensions of impeachment seriously—and to leverage the inevitable theater of the conflict toward salutary ends.

If impeachment is the most serious way that Congress holds the president in check, then elections are the way voters hold both the president and Congress in check. As I’ve argued before, for impeachment to work, citizens have to be brought into the process. They have to make their voices heard by elected officials so that Congress does the right thing. And, importantly, there has to be an electoral cost to politicians that aid and abet a lawless president.

Fortunately for the electoral prospects of Democrats, the Republicans are tying themselves to the mast of Trump’s criminality. Even as the Senate trial got started, a torrent of news validated the decision to impeach.

On Thursday, The Government Accountability Office released its finding that the Trump administration violated the law by withholding military aid that had been authorized by Congress. The previous night, Lev Parnas, a businessman and crony of Trump lawyer Rudy Guiliani, gave an interview on MSNBC to Rachel Maddow where he verified and elaborated on the case against Trump. To be sure, Parnas is a dubious character, one facing criminal charges, but he is also undeniably part of the circle that pursued Trump’s agenda in Ukraine. At the very least, his claims deserve to be investigated.

Some Republicans, including Maine Senator Susan Collins, appear open to the Senate’s calling witnesses. But a wider cohort of the party is eager to bind themselves ever tighter to Trump. Appearing on Fox, Lindsey Graham said, “I’m going to judge the case based on the evidence found by the House. I’m not going to expand the record. This Parnas thing, I smell a rat.” Graham added, “I don’t take Chuck Schumer seriously when he says he’s looking for the truth. He’s looking to get back to be the majority leader. Nothing more.”

On another Fox program, Reince Priebus, former chief of staff at the White House, said, “Sometimes the best defense is the ‘so-what’ defense which is, if everything the Democrats said is true it’s still not impeachable. If everything Lev Parnas said is true, it’s still not impeachable.”

The behavior of the GOP creates an opportunity for the Democrats. A sizable cohort of Senate Republicans up for reelection are now finding themselves vulnerable as they navigate through the process of defending an unpopular president.

Summing up recent polls they conducted, Morning Consult concluded, “All five of the most vulnerable Senate Republicans head into the trial with voters in their states either souring on their job performance or with perceptions of the president threatening to pull them further down.”

The polling agency adds, “The former applies to Sens. Martha McSally (R-Ariz.) and Susan Collins (R-Maine), whose respective 5- and 4-percentage-point declines in their net approval rating between the third and fourth quarters of 2019 put them a respective 3 and 10 points underwater.” Other Republican senators facing polling trouble are Colorado’s Cory Gardner, Iowa’s Joni Ernst, and North Carolina’s Thom Tillis.

These vulnerable Republicans have to keep their Republican base convinced that they are loyal to Trump while also creating enough distance with Trump to satisfy the larger electorate.

For Democrats, going after these Republicans is a way of fulfilling a constitutional duty while also engaging in shrewd politics. Continued pressure on vulnerable lawmakers could yield a more tractable Senate that calls witnesses and continues investigating Trump. If such cooperation isn’t forthcoming, there’s ample opportunity to target these senators.

The crucial point Democrats have to remember is that impeachment is not an apolitical activity. Politics is an essential tool for making impeachment effective and imposing real penalties on a lawless president and his partisan accomplices.