The only certainty about tax reform is uncertainty. That’s the recipe for the next few weeks on Capitol Hill.

Congress is entering a sprint to finish tax reform -- and it’s barely started. House Speaker Paul Ryan, R-Wis., wants to wrap up tax reform before Christmas. But House Freedom Caucus Chairman Rep. Mark Meadows, R-N.C. , has another idea:

“Vote on this before Thanksgiving,” Meadows, the leader of the conservative caucus, said during a recent Fox News interview.

Trade in tinsel and wrapping paper for cornbread and stuffing.

Maybe had members of Congress really stepped on the gas, they could have had it done before Canadian Thanksgiving. But that came two weeks ago.

The reason for the sprint? Several wild cards could upend tax reform if congressional Republicans don’t move expeditiously. That’s where uncertainty enters the picture.

Consider the Senate vote Thursday night to adopt a budget framework for tax reform. That budget blueprint wasn’t so much about spending priorities as it was about granting the chamber a special parliamentary tool known as “budget reconciliation” with which to tackle tax reform.

Senate Republicans can’t overcome a filibuster on tax reform. But budget reconciliation eliminates filibusters and requires only a simple majority of senators to clear the final hurdle. (That’s 51 yeas if all 100 senators vote.) But the roll call tally on the budget framework plan was tight: 51-49.

Sen. Rand Paul, R-Ky., was the lone GOP nay. Lose another Republican and it’s 50-50. That would require Vice President Pence to cast the tie-breaking vote. However, tax reform is dead if another Republican drops off.

So here are three variables that could imperil tax reform:

The health of GOP Sens. Thad Cochran, Mississippi, and John McCain, Arizona, and the special election in Alabama on Dec. 12 to succeed Sen. Luther Strange, R-Ala. Conservative Roy Moore defeated Strange in the GOP primary. Moore will touch gloves with Democrat Doug Jones for the right to come to Washington.

Let’s start with Cochran.

Cochran had been absent from Washington for weeks suffering from health issues. His office declared Cochran would be back after treatment for a urinary tract infection.

Then Cochran’s staff announced early he wouldn’t return. That put adoption of the budget on a tightrope. A day later, Cochran’s team backtracked and said the senator would be in Washington to vote.

Cochran has appeared increasingly feeble of late. He’s chairman of the Senate Appropriations Committee and rarely provides reporters with in-depth answers when asked questions in the hall -- a stark contrast to how Cochran formerly engaged scribes.

Cochran returned Tuesday, guided by an aide, to the Senate chamber. I asked Cochran if congressional leaders rousted him from his sickbed because his vote was crucial to approve the budget.

“It’s a beautiful day outside,” he replied.

The non sequitur reply may have been a precursor as the senator sat quietly at his desk in the chamber, rarely engaging fellow senators.

During one roll call, the aide nudged Cochran to vote as he had apparently forgotten to do so. Cochran appeared to struggle to raise his left arm in the air to signal either thumbs up or thumbs down -- the Senate custom to record one’s vote.

On the next vote, the clerk read the Senate roll in alphabetical order. Cochran’s name falls between Sens. Bill Cassidy, R-La., and Susan Collin, R-Maine. When the clerk hit Cochran’s name, the senator immediately raised his hand and hollered “aye.” The aide then elbowed Cochran and could audibly be heard in the chamber saying “no. no.”

At the behest of his aide, Cochran then switched his vote to nay. There was a brief pause in the calling of the roll as the clerk corrected Cochran’s ballot on the tally sheet.

It’s not uncommon for senators to vote “incorrectly,” then switch their vote. That’s especially true during the Senate’s “vote-a-rama.” That’s when senators take vote after vote -- sometimes for hours on end -- trying to finish the budget. It’s also routine for senators to rely on aides to follow proceedings and “coach” them on how to vote.

But Cochran’s performance provoked lots of murmuring in the Capitol and raised questions as to who was calling the shots.

Cochran disappeared for a couple of hours and missed a few votes during the vote-a-rama. Had Cochran been absent, the Senate would have adopted the budget framework for tax reform 50-49. That’s pretty close. It shows there’s no margin for error for Republicans on tax reform.

McCain’s been back in Washington for weeks now, after missing time for brain cancer treatment. He’s appeared vigorous, tangling with reporters in the hallways and even threatening the Pentagon with subpoenas following the ambush of U.S. forces in Niger. But his health issues forced Senate Majority Leader Mitch McConnell, R-Ky., to postpone work on an effort to repeal and replace ObamaCare for a period in July.

That was the case until McCain returned to work -- and promptly voted to torpedo the measure.

The Alabama special election also bears watching. The campaign of GOPer Moore indicated to Fox on Friday that it had no guidance on how the nominee would vote on tax reform should he win in December. But later, Moore spokesman Drew Messer told the cable news network that “Moore is all in on working with President Trump on tax reform.”

That said, some GOP Senate sources fear Moore may be too conservative to vote for the final tax reform product, if he win a ticket to Washington. By the same token, other sources told Fox that Democrat Doug Jones may even be in play should he emerge victorious.

The theory is that a moderate Democrat like Jones may have to work exhaustively across the aisle if he is representing a red state like Alabama. What better way to do that than on tax reform.

A Fox News poll last week showed the race in a dead heat between Moore and Jones.

But wait. There’s more.

What happens if Sen. Bob Menendez, D-N.J., is convicted in his corruption trial and is forced to resign? There is a narrow window under which New Jersey Gov. Chris Christie, a Republican, could appoint a fellow GOPer to the Senate if Menendez leave office prior to the end of Christie’s term next year.

Another Republican in the Senate could help the GOP on tax reform. But what if a potential Republican senator from New Jersey opposes the package because it kills deductions for state and local taxes, a big issue in a tax-burdened place like New Jersey.

So, the race is on for Republicans to knock out tax reform as quickly as possible before they face other quandaries.

That’s why House Republicans are aiming to vote this week to align themselves with the Senate budget. That paves the way for House Ways and Means Committee Chairman Kevin Brady, R-Texas, to post prospective bill text around the first of November.

Brady would then hold a “markup” session in which lawmakers retrench the bill in committee. Some House Republicans would then like to race the plan to the floor before Thanksgiving.

Of course, who knows what would happen in the Senate. And it’s unclear if the House and Senate could ever match up their own tax bills -- provided that both chambers can approve something expeditiously.

People may grouse that the devil may be in the details on tax reform and that could slow matters. True. But Republicans may be so desperate to pass anything that in a strange way, the details may not matter. That could be especially true if Congress is under the gun to wrap up by Christmas.

The conundrums Republicans could face aren’t new when it comes to dealing with major legislation.

Democrats had 60 votes to overcome all sorts of Senate filibusters when they prepared to advance ObamaCare in 2009. Then-Sen. Ted Kennedy, D-Mass., passed away. In 2004, the Massachusetts legislature changed the rules to prevent then-Gov. Mitt Romney, a Republican, from appointing a Republican to the Senate should then-Sen. John Kerry, D-Mass., win the presidency.

But the Massachusetts legislature reversed course after Kennedy’s death so then-Gov. Deval Patrick, a Democrat, could quickly appoint a fellow party member. Patrick tapped Sen. Paul Kirk, D-Mass., to serve as a caretaker senator until there was a special election in January 2010.

Kirk’s appointment helped Democrats preserve operational control of the Senate to pass the first version of ObamaCare. Democrats beat back repeated Republican efforts to filibuster, holding their 60-vote Senate supermajority.

But things changed in January, 2010. That’s when then-Sen. Scott Brown, R-Mass., upset Democratic nominee Martha Coakley in the special election. Democrats suddenly held only 59 Senate seats and could no longer quash Republican filibusters with the necessary 60 yeas.

As a result, Democrats employed some parliamentary wizardry and finished ObamaCare in March 2010. They did so using the special budget reconciliation process that sidesteps filibusters.

This is why Senate Republicans needed to approve a budget so badly. No budget? Then no budget reconciliation process for tax reform. Tax reform would be stuck.

The budget vote-a-rama last week was tame compared to other voting fests that drag on for 12 to 15 hours. The Senate chopped up this vote-a-rama into short tranches. The best way to gauge the intensity of such a vote? Pizza.

This was only a “four pizza” night. Reporters observed aides wheeling only four Ledo’s pizzas into McConnell’s office vote session, which wrapped up just before 9:40 p.m. Other vote-a-ramas may require as many as 15 or 20 pizzas. The roll call votes may not wrap until 3 or 4 in the morning.

McConnell spokesman Don Stewart contested the four pizza observation. He declared it to be “fake news” and tweeted out a picture of 18 Ledo’s pizza boxes stacked up in the leadership suite.

Four pizzas or 18 pizzas? Perhaps that reflects “dynamic scoring.” Dynamic scoring is the controversial actuarial method Republicans are using for tax reform to demonstrate it won’t explode the deficit.

Just one more variable to consider as congressional Republicans try to rush through tax reform before the end of the year.