House Speaker Paul Ryan has urged Congress to move quickly to enact Donald Trump’s sweeping tax cuts and “give the president his first major legislative win.”

“Securing passage by Congress of the tax plan would give President Donald Trump his first major legislative win since he took office in January,” Ryan told Reuters in an interview Wednesday.

Ryan’s remarks come as corporate lobbyists descend on Capitol Hill to pressure lawmakers to approve the proposed massive tax breaks.

”When the details come, that is when you’re going to see K Street coming to Congress. And that’s why this hasn’t been done for 31 years,” said Ryan, looking back to the country’s last major tax changes under President Ronald Reagan in 1986.

While Republicans control the White House and both chambers of Congress, Ryan admitted that the tax proposal is entering most difficult phase and Republicans are under pressure to deliver on their election campaign promises.

Ryan referred to white-water rafting to describe how the tax overhaul effort is entering its toughest phase, which he compared to fast-flowing Class 5 rapids on a river.

“We’ve been going through Class 3 rapids, which is a pleasant ride. It’s nice. Everybody pretty much stays in the boat and it’s pretty good. But we’re about to go through Class 5 rapids, which is the biggest rapid you can go through,” he said.

He called on Republican lawmakers to stand firm as details of the legislation are hammered out, and predicted that some Democratic lawmakers would eventually back the tax plan.

“At the end of the day, I do believe some Democrats will end up voting for this thing,” Ryan said, according to Reuters. “It’s hard for me to see why – no matter what party you’re from – you’d want to vote against this.”

A key element of the Trump plan is to slash the corporate income tax rate to 20 percent from 35 percent.

Democrats have condemned the tax plan as “a gift to the rich” and to corporate America that would cause the federal deficit to balloon and add to the $20 trillion U.S. national debt. ShareTweet