This post has been updated with the latest news.

After Senate Republicans passed a tax bill earlier this month, Republicans were only halfway through the process. They still had to merge the Senate and House versions into one tax bill that could pass both chambers all over again.

It looks like they're coming close to that.

The Post's Damian Paletta and Erica Werner report that on Wednesday, House and Senate Republican leaders reached an agreement on the central component of the tax bill, how much to lower the corporate tax rate. They will lower it to 21 percent, something President Trump immediately said he'll support.

Here are the steps Republicans must still navigate to get tax revisions done, and where they could fall short.

1. Pass a budget resolution through the House: Done. Congress has budgeted $1.5 trillion in tax cuts, a remarkably high number for a party that tries to position itself as the fiscally conservative one. The merged bill maintains that price tag.

2. Write a tax bill:  Done. Well, technically there are two bills, one written by House Republicans and the other written by Senate Republicans. Republican leaders are in the process of merging the two, because only one bill can be sent to President Trump's desk. (More on this in step five.)

3. Vote on it in the House: Done. The House's tax bill passed with a comfortable margin among Republicans; all but 13 House Republicans voted for it, which is less opposition than expected after intense intraparty debates about how much to cut popular middle-class deductions, such as the mortgage interest rate or state and local taxes.

4. Vote on it in the Senate: Done. Even though about a dozen Republican senators had competing concerns with the bill, in the end all but one Republican  — Sen. Bob Corker (Tenn.) — voted for it.

Procedurally, Republicans are following the same path they used to try to repeal the health-care law without Democratic votes, which means this whole endeavor could be shut down by a few “no” votes from GOP senators.

Senate Republicans could only afford two defections. But if this vote gets delayed for any reason after Alabama's newest, Democratic senator gets seated, Republicans can only afford one defection. And that spot appears to be taken up by Corker, who said he was concerned the bill could raise the deficit too much. In other words, Senate Republicans have no room for error when the merged bill comes back to their chamber.

5. Merge the Senate and the House bills — and pass it:  Almost done.  A vote on this merged bill, called a conference report, could happen in both chambers as soon as next week.

The two tax bills that have passed each chamber of Congress have some significant differences.. The House bill gives much larger tax cuts to businesses  (in the form of “pass-throughs”) as well as the ultra wealthy (in the form of repealing the estate tax) than the Senate bill does.

Lawmakers and lobbyists have spent the past two weeks trying to merge the very different bills behind closed doors. On Wednesday, they announced they agreed on a component of the bill that could allow everything else to fall into place: how much to lower the corporate tax rate (from 35 percent to 21 percent) and the tax rate for wealthy individuals (from 39.6 percent to 37 percent).

Negotiators also said they agreed to allow Americans to deduct more state and local taxes, which could satisfy moderate House and Senate Republicans from states like California, New York and New Jersey.

Hovering above all these negotiations is a strict price tag. If Senate Republicans want to avoid a Democratic filibuster, they have to keep the tax bill costing $1.5 trillion over 10 years, and not a penny more. (I explain that process, called reconciliation, here.) Looks like lawmakers kept this all within that price tag, as well.

6. Get Trump to sign it:  This may actually be one of the most iffy steps, because Trump has not proven himself a reliable dealmaker.

And Republicans are not relying on Trump to be consistent about what he wants in a tax bill.  Gours after the bill passed the Senate earlier this month, Trump suddenly signaled he'd be open to a higher corporate tax rate, which could potentially throw the whole negotiation off balance.

But on Wednesday, another major break for Republicans in this precarious process: Trump said Wednesday that he supports the agreement they've come to.

In the end, the pressure to get a major legislative victory could bring everyone in line. Republican lawmakers are almost a year into governing Washington and have no major legislative wins. Failure to pass tax revisions “will be the end of us as a party,” Sen. Lindsey O. Graham (R-S.C.) warned in an interview with the New York Times. Behind the scenes, other Republicans agree.

That doesn't mean these last few steps are going to be easy.

“All this revolves around two things,” said Steve Bell, a former GOP Senate budget aide. “GOP desire to have done 'something' before the 2018 elections and Trump's desperation to sign a tax cut in a Rose Garden ceremony.”

It looks like that Rose Garden ceremony could be coming, as soon as next week.