“At different times the president has expressed different views. But I wouldn’t get too distracted by an intervening tweet,” said Sen. John Cornyn (R-Texas), who is close to Senate Majority Leader Mitch McConnell.

“This is about Chuck Schumer getting 2020 Republican incumbents into tough voting situations,” Cornyn added in reference to Schumer’s vow to force motions to subpoena witnesses. “It won’t surprise you that we’re thinking about that too and how to avoid that as much as possible.”

The GOP has tried to stay focused on its game plan to shut down Democratic hopes of locking in witnesses at the outset of the trial, but it’s become increasingly clear the party will face an internal reckoning during the trial as it defends its Senate majority and faces a president who demands complete loyalty.

Sen. Susan Collins (R-Maine) has sent GOP leaders a message that they can’t assume she will try to move through the trial as quickly as possible and ignore the possibility of hearing new evidence. And she’s not alone.

Take Sen. Lamar Alexander (R-Tenn.), who is retiring at the end of the year. He says he might vote to hear witnesses “if I needed to. Or I might not. Or I might.”

“My view is we should hear the case, ask our questions and then have a vote on whether we need to hear additional witnesses or call for additional documents,” said Alexander. “It’s important to have a vote on whether we have witnesses or not.”

Republicans are preparing a resolution establishing trial rules that would punt those decisions until after hearing the opening arguments from House impeachment managers and Trump’s attorneys. McConnell (R-Ky.) is expected to finalize that language on Tuesday with his conference, and it will be “substantially similar” to the language governing former President Bill Clinton’s impeachment trial, according to a person familiar with discussion. Ultimately in that trial, the Senate subpoenaed three witnesses for depositions after opening arguments.

McConnell has to balance his approach to the Trump trial between GOP hard-liners who want an immediate vote to dismiss the case and his more moderate members, such as Collins, Lisa Murkowski of Alaska, and Mitt Romney of Utah, who want to retain the ability to call witnesses for additional evidence.