House Republicans celebrate passing a tax bill on Nov. 16. (Chip Somodevilla/Getty Images)

This post has been updated with the latest news.

House Republicans passed a tax bill this week, crossing off a big item on their to-do list. But there are still a number of steps Republicans need to take to make the first comprehensive tax bill in three decades a reality, and it only gets more difficult from here.

Big pieces of legislation have fizzled at this step in the legislative process as recently as the summer. The Senate failed to pass an Obamacare repeal after the House passed its own. Even if the Senate could pass a tax bill this time around, there's no guarantee it's something both chambers could agree on and send to the president's desk.

Procedurally, Republicans are following the same path they used to try to repeal Obamacare without Democratic votes. That fell short by one vote in the Senate in the summer. That means this whole endeavor could hinge on a few “no” votes from Republican senators.

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

1. Pass a budget resolution through the House of Representatives: Done. Congress has now budgeted $1.5 trillion in tax cuts, a remarkably high number for a party that tries to position itself as the fiscally conservative one.

2. Write a tax bill:  Done. Well, technically there are two bills, one written by House Republicans and another written by Senate Republicans. That's a problem, since Congress can only send one bill to President Trump's desk.

The two bills have some significant differences that could derail their chances in either chamber. The Senate bill eliminates all state and local tax deductions, for example, while the House still allows it up to $10,000.

3. Vote on it in the House: Done. On Thursday, 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, like the mortgage interest rate or state and local taxes.

The bill permanently cuts taxes for corporations and temporarily cuts the tax rates for individuals, though Republicans are betting on a future Congress extending those.

Republicans were expected to get this far on taxes; they got this far on trying to repeal Obamacare. But the next few steps are the most precarious.

4. Vote on it in the Senate:  The same divisions on taxes in the House are exacerbated in the Senate. Will conservatives oppose a bill that blows a hole in the deficit? Will moderates be repelled by the fact that most of the tax breaks go to corporations and the wealthy, which leaders hope will spill down to the rest of America? And what about the fact the Senate bill tries to repeal the Obamacare individual mandate, potentially leaving millions of Americans uninsured?

Republicans can only afford two defections, since no Democrat is expected to vote for the bill. Already, Sen. Ron Johnson (R-Wis.) has said he won't support the bill as is because he thinks it favors big corporations over smaller businesses. Sen. Susan Collins (R-Maine), a key vote, said all week it's a “mistake” to inject health care into a tax bill. A number of other senators haven't explicitly supported the bill.

It's worth saying again: Republicans can afford only two defections. This is why an Obamacare repeal effort died.

Sen. John McCain (R-Ariz.) on July 28 voted against the Republican "skinny repeal" health-care bill. (U.S. Senate)

5. Make sure it's the same bill: A bill that passes the House is rarely the same that passes the Senate. Lawmakers will have to find a way to create a hybrid of the bills that can pass both chambers again. That's going to be difficult, because as The Post's Mike DeBonis and Damian Paletta point out, the House bill was cobbled together to pass a chamber of specific lawmakers with specific interests. One change could throw the whole bill off balance in the House, and vice versa.

6. Get Trump to sign it:  Trump changed his position on a bipartisan health-care bill half-a-dozen times in ONE day. Republicans are not relying on Trump to be consistent about what he wants to see in a tax bill. Lawmakers originally flat-out ignored his demands to leave 401(k) plans out of the bill, though the Senate did decide to try to undo the Obamacare individual mandate, like Trump wanted.

(Jabin Botsford/The Washington Post)

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

GOP operatives trying to help Republicans keep their majorities in Congress say a bill that cuts middle-class taxes without blowing a hole in the deficit would be much easier for them to sell.

“Politically this is, always has been, and always will be the most important issue,” said Corry Bliss, head of a House GOP super PAC. “There's nothing more important than having a good-paying job and being able to provide for your family.”

That doesn't mean this is going to be easy.

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