The White House and the Senate's top Republican said Friday they have enough votes in place to pass the sweeping Republican tax reform bill which could hit the floor for a final vote in a matter of hours, as key holdouts announced their support.

While GOP leaders were still seeking additional support, 50 votes is enough to get the historic tax plan across the finish line in the chamber. The measure would lower the corporate tax rate from 35 percent to 20 percent and double the standard deduction for individuals and families, among other things.

"We have the votes," Senate Majority Leader Mitch McConnell said.

Moments later, Sen. Jeff Flake, R-Ariz., one of the last GOP holdouts, said he was prepared to vote for the bill.

Approval would be a major victory for the Trump administration.

“Republican Senators are working hard to pass the biggest Tax Cuts in the history of our Country. The Bill is getting better and better. This is a once in a generation chance. Obstructionist Dems trying to block because they think it is too good and will not be given the credit!” President Trump tweeted early Friday.

Sen. John Cornyn, R-Texas, the No. 2 Senate Republican, also said Friday they are "confident in the 50" and are trying to build on that, the Associated Press reported.

If they reach 50 votes exactly, Vice President Pence would be needed to break a tie. Once it passes, the bill would go to a conference committee where key Senate members would reconcile it with a House version passed Nov. 16.

The last GOP holdout Sen. Bob Corker, R-Tenn., who has sparred publicly with Trump and voiced objections to increasing the deficit, announced Friday afternoon he would vote against the bill.

“I wanted to get to yes," Corker said in a statement. "But at the end of the day, I am not able to cast aside my fiscal concerns and vote for legislation that I believe, based on the information I currently have, could deepen the debt burden on future generations.”

MCCAIN TO VOTE FOR SENATE TAX REFORM BILL

But McConnell, R-Ky., was able to garner the support of a handful of key GOP senators.

Sen. Ron Johnson, R-Wis., initially was the first Republican senator to oppose the tax reform package -- but Friday, Johnson’s spokesman told Fox News he flipped to a “yes” vote. Johnson’s support came after negotiating an improved treatment for pass-through entities, which account for about 95 percent of U.S. businesses.

Pass-through businesses are not corporations, and therefore aren’t taxed as such. They include sole proprietorships, joint ventures and limited liability companies. The owners often declare the profits on their personal tax returns.

“There’s a lot of work to be done to reconcile the treatment of pass-throughs in the Senate and House bills, and I am glad to have received assurances I will have a seat at the table during those negotiations,” Johnson said in a statement Friday.

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According to Johnson’s office, under the agreement, the deduction for pass-through businesses will increase from 17.4 to 23 percent, and additional steps are expected to be taken to ease the transition for businesses to different statuses.

Sen. Steve Daines, R-Mont., also initially wavered on the bill, but said he would vote in favor on Friday on “Fox & Friends.” Pence hosted Daines, along with Flake, Sens. James Lankford, R-Okla., and David Perdue, R-Ga., for dinner Thursday night to discuss tax reform, and seemingly pulled Daines over the line.

But GOP leadership was optimistic the tax bill would pass beginning early Thursday when key votes -- Sens. John McCain, R-Ariz., and Lisa Murkowski, R-Alaska -- announced their support.

“I believe this legislation, though far from perfect, would enhance American competitiveness, boost the economy, and provide long-overdue tax relief for middle-class families,” McCain said in a statement Thursday.

Republicans only have two votes to spare in the Senate, where they hold a 52-48 edge.

McConnell invited members to a meeting Friday morning to review potential substitute amendments, and will move to debate on the Senate floor, followed by what the leader’s office is calling a vote-a-rama.

Fox News' Blake Burman and Mike Emanuel contributed to this report.