But there are already signs of pushback from Republicans, who worry about breaking with Trump in the border wall fight, and Democrats, who are skeptical of signing onto the letter without a firm grasp on GOP support.

"I hope by the end of today we have a robust, bipartisan letter that we can deliver to the president. But you've sure got people who are pushing back in their caucus and that's striking to me,” Coons, referring to Republicans, said after a closed-door lunch Wednesday.

Coons added that if those pushing for the letter can’t get enough support then it was his “view” that they wouldn’t send it at all, though he caveated that it could just be delayed until after Wednesday and that Republicans are still reviewing a draft of the letter and asking questions.

The letter is the latest effort by a group of centrist senators to break the entrenched stalemate between Trump and congressional Democratic leadership, as the shutdown is in Day 26 with no clear path toward an agreement.

Lawmakers in the letter ask Trump to support a three-week continuing resolution (CR) in exchange for taking up his border wall request as a supplemental appropriations bill, according to senators who have signed onto it.