After months of painstaking negotiating internally and externally, President Trump signed the United States-Mexico-Canada Agreement in a large ceremony at the White House Wednesday, a significant achievement for the trade-minded president. But it was clear the Senate impeachment trial was at the forefront of the president's mind.

Republican members of the House and Senate, particularly those who have been the most vocal in defending the president throughout the impeachment process, were seated in the front rows. As the president praised Republicans present, he joked that maybe he's just being nice to senators because he wants their votes to acquit him in the Senate impeachment trial.

"I want to just if I could mention, because we do have some incredible people that work so hard, and uh, senators. Maybe I'm being just nice to them because I want their vote. Does that make sense?" the president said, to laughter. "I don't want to leave anybody out. Hey congressmen, I already got your vote, 196 to nothing. To hell with you."

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The president also joked that Senator Ted Cruz probably has some interesting questions to ask when senators get their first crack at the Q&A session starting Wednesday afternoon, after days of being forced to listen to both sides in silence.

"He's dying to get back there and ask those questions," Mr. Trump said of Cruz. "He's got some beauties, I'll bet."

Senators will have 16 hours to submit their written questions. The Q&A period is likely to be finished Thursday.

Later in the ceremony, the president made sure all the senators present were on stage for the actual signing, joking more than once that he would make sure he took care of senators.

"I don't care about anybody else," the president could be heard saying as he made sure Republican senators were on stage with him.

The recognition that there could be enough Republican votes to call for witnesses in the president's impeachment trial has sent the White House scrambling. A senior administration official involved in impeachment strategy said the White House has always feared four Republicans could break with them, and the White House needs to reduce that number by half.

"We need to chisel four down to two," the official said. "We are comparing notes with the leader's office. I would say we are at DEFCON 2."

No Democratic members of Congress were listed on the White House's list of expected attendees, nor were any Democratic members of Congress visible, and it's unclear whether any were invited.

Mr. Trump said farmers, who have been hit by the trade war with China, will be huge beneficiaries of the USMCA. The president made the announcement outside the White House's East Wing, separated from reporters and attendees by a driveway, making it nearly impossible for reporters to lob questions.