Support for obtaining new documents at the trial is “even stronger than we thought, with large numbers of Republicans supporting it,” Schumer (D-N.Y.) said in an interview. “And when you go against what the American people feel strongly about, on an issue they’re paying attention to, it’s not a good idea.”

Public surveys in key swing states back up Democrats’ claims.

Polling from Hart Research found that 63 percent of voters in Arizona, Colorado, Maine and North Carolina would react unfavorably if their senator voted against calling witnesses or subpoenaing documents during the Senate impeachment trial. Another poll from Morning Consult found 57 percent of voters believe the Senate should call additional witnesses. That includes 71 percent of Democrats, 56 percent of independents and 40 percent of Republicans.

Given Trump’s fast-paced presidency, there’s no guarantee impeachment is the top issue for voters in November.

But Maine moderate GOP Sen. Susan Collins is already moving to blunt Schumer’s tactics, which she has complained about bitterly. She says she’s working with a handful of Republicans to keep a pathway open for witnesses, flashing some independence from Trump and McConnell.

“I am hopeful that we can reach an agreement on how to proceed with the trial that will allow the opportunity for witnesses for both the House managers and the president’s counsel if they choose,” Collins said in a statement for this story. “It is unfortunate that Chuck Schumer — who voted against witnesses in the Clinton trial and prejudged its outcome — and his allies are seeking to politicize this process.”

Trump national security adviser John Bolton’s offer to testify gives some momentum to Democrats' calls for witnesses and documents about the White House’s decision to withhold aid to Ukraine. Democrats also want to hear from acting White House chief of staff Mick Mulvaney, Office of Management and Budget official Michael Duffey, and Mulvaney adviser Robert Blair.

“If the Republicans ram through process that ultimately leads to no witnesses, I think they do it at their own peril,” said Sen. Robert Menendez (D-N.J.), a former chairman of the party’s campaign arm. “Some of these members: They have an audience of one. But I think they forgot that there’s a broader audience that they’re going to have to face at election time.”

Republicans say Schumer has the politics all wrong, and that they are merely following the precedent of President Bill Clinton’s trial. That means starting the trial and deciding on witnesses later. However, Clinton impeachment investigators in 1999 did not face the same level of stonewalling the House has faced to date from Trump and Senate Republicans and eventually sought testimony from key witnesses.

So now that Schumer’s proposal has been rejected, Republicans merely see an effort to save face.

“He can create that narrative, I’m not the least bit worried about it,” said endangered Sen. Thom Tillis (R-N.C.). “Sounds like he’s trying to make lemonade out of lemons.”

“Everybody believes Sen. Schumer’s going to play a game with impeachment to try and get back the Senate,” said Sen. Lindsey Graham (R-S.C.), who is also up for reelection. “He wakes up every day trying to be the majority leader.”

Yet concentrating on process may also be good politics for Democrats.