In an aside to his announcement Thursday that the U.S. will leave the Paris climate agreement, President Trump said the administration's tax bill is proceeding "very well" in Congress, although no legislation has been introduced.

"Our tax bill is moving along in Congress, and I believe it's doing very well," Trump said at Thursday's event in the White House Rose Garden. "I think a lot of people will be very pleasantly surprised.

"The Republicans are working very, very hard," Trump added. "We'd love to have support from the Democrats, but we may have to go it alone. But it's going very well."

Congressional Republicans are engaged in talks with the Trump administration to draft a single, unified tax reform measure that they can move through the House and Senate. Those efforts are expected to pick up next week, when Congress returns from its week-long Memorial Day break. To date, however, no tax bill has been introduced. For its part, the Trump administration has released only a single page of bullet-pointed tax principles.

Some outside supporters have faulted Trump and the GOP for the slow pace of action on tax reform. Trump, too, has expressed impatience with the legislative schedule. This week, he called on Twitter for the Senate to move to a 51-vote threshold for legislation to approve "tax cuts ... fast and easy."

In trying to clarify that tweet Tuesday, White House press secretary Sean Spicer said that "the frustration that he's had with the pace of some of the legislation and some of the obstructionist tactics that Democrats have employed, whether it's Cabinet nominees or other pieces of legislation, has been well documented."