More: The housing bill would still become law without Trump's signature in 10 days after Congress formally submits the bill. He did not threaten to veto the measure. It's not clear if a president has ever refused to sign a bill he supported in similar circumstances before.

Thune seemed stunned by Trump's announcement that he wouldn't sign the bill.

"I just heard that. I guess I would say, at this point, I don't have any observations about that," he told reporters.

Shortly after the announcement, workers began dismantling a stage set up in the Capitol for a signing ceremony and removing the presidential seal from the lectern where Trump had planned to speak.

Warren said she had no idea if Trump would let the bill become law. He supported the measure from start to finish, especially the private equity provision that Warren championed. He'd even mentioned it in his State of the Union address on his prior visit to the Capitol.

"Don't ask me to rate Donald Trump's tantrums. That's not my specialty," she said.