The Republican plan to slash corporate and personal income taxes has finally begun moving forward in Congress, and President Donald Trump wants lawmakers to act with haste.

In a tweet Wednesday, Trump urged Republicans to “move fast” on what he said would be a massive tax cut.

“The approval process for the biggest Tax Cut & Tax Reform package in the history of our country will soon begin,” Trump tweeted. “Move fast Congress!”

The tweets came as forward progress appeared to begin on the tax overhaul.

Trump is reportedly set to launch into a prolonged cross country tour to advocate for the cuts. Other White House officials, most notably Treasury Secretary Steven Mnuchin, have already been taking their case to the public to drum up support.

Separately, the tax-writing committees in Congress are holding a series of hearings on tax proposals and plan to release fully fleshed-out legislation by the end of the month.

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Trump also hosted a dinner of bipartisan senators on Tuesday, meeting with Democratic senators in states he won in 2016. The president likely will pressure those lawmakers, especially ones up for reelection in 2018.

However, significant elements of the plan still need to be hashed out, and the rapport between the White House and Congress – even within the Republican Party – may be at a low point. The process for passage – Republicans would need to win over eight Senate Democrats or move through the complicated process of reconciliation – could mean that Trump’s beckoning is easier said than done.