Washington (CNN) On Tuesday afternoon, Senate Republicans made the biggest decision of the 2018 election to date: They put a repeal of Obamacare's individual mandate into their tax cut package .

The move was done out of a combination of necessity and political calculation. Repealing the individual mandate creates more than $330 billion in deficit reduction -- an irresistible sum for a party desperate not to blow a massive hole in the deficit with their tax plan -- and it also offers the possibility of (sort of) making good on an eight-year long campaign pledge to their base to get rid of Obamacare.

There's just too much potential there -- in terms of the policy and the politics -- for Republicans not to leap at it.

But make no mistake: Like anything with a major upside, this gambit is also a massive risk for Republicans. By combining the tax cut bill and the repeal of the individual mandate, Republicans are going for broke -- legislatively and politically.

If this succeeds, they have not one but two major legislative accomplishments to point voters to as they campaign in 2018. If its fails, they will have zero legislative accomplishments to take to voters. That lack of tangible results -- together with President Donald Trump's unpopularity, historic midterm trends for the party that holds the presidency and the double-digit edge Democrats currently enjoy on the generic ballot -- would spell near-certain doom for Republicans next November.

Think of it this way. Republicans are down three runs in an elimination game in the World Series. They have the bases loaded. Their batter has two strikes against him. Rather than choking up on the bat and just trying to make contact, Republicans are taking a massive cut at the ball. Which means they will either make solid contact and drive the ball over the fence -- winning in dramatic fashion -- or they will swing and miss so hard that they throw the bat into the stands and fall over, ending the game and their season.

Which is it going to be?

Congressional Republicans insist they are confident that they have the votes, according to CNN's Phil Mattingly . It's not entirely clear whether that confidence is merited given that the addition of the repeal of the individual mandate hasn't been in the bill for even 24 hours and the Senate and House bills have several notable differences that would need to be reconciled.

Past experience -- particularly as it relates to health care reform -- would also suggest caution is warranted. Already this year, Republicans have tried and failed twice in the Senate to gather the necessary votes to repeal Obamacare. Each time, a handful of senators -- Lisa Murkowski (Alaska), Susan Collins (Maine), John McCain (Arizona) and Rand Paul (Kentucky) -- have doomed those efforts. (Republicans hold only a two-seat Senate majority, meaning they can only afford to lose two GOP senators on any bill and still hope to pass it.)

But McCain sent positive signals about the bill on Tuesday afternoon and dismissed concerns about adding the individual mandate repeal to the legislation. And adding the repeal will likely entice Paul -- and assuage enough of his concerns about the deficit. That would allow Collins and Murkowski to vote against the bill and still have it pass the Senate, which is further than most Republicans thought they could get on any sort of health care effort even a month ago.

The fate of the legislation is less certain in the House, where a potential revolt by northeasterners whose states would be disproportionately impacted by a provision that would jettison the ability to write off state and local tax payments awaits. But, at the moment, congressional Republicans are more optimistic than they have been in months about the possibility of a major piece of legislation passing.

The hardest part, of course, may not be passing the bill but rather selling it as a good thing for the country.

Two numbers complicate that selling effort. The first is 13 million, which is the estimate of how many people will lose health care coverage over ten years if the individual mandate is repealed. The second is 10%, which is the estimated premium increase for people with health insurance in the majority of the 10 years that the bill covers.

Politically speaking, those will be tough hurdles. While people may not love Obamacare, it's the devil they now know. Passing something that gets rid of a major component of the Affordable Care Act and replacing it with something unknown will make lots of people -- including even some loosely-affiliated Republicans -- skittish.

And, when it comes to premium increases, well, no one likes to pay more money for something.

Republicans will seek to offset those concerns by touting the power of the free market and by reminding people that the tax cuts are delivering more money to their pockets -- to spend on what they see fit.

Which isn't a terrible argument. People like getting money back!

The question for Republicans is whether they can convince people that the gains made by reducing taxes are worth the pain caused -- at least to some -- by getting rid of the individual mandate. And that fight presumes they can get the bill passed, which, as I noted above, is no sure thing.

What Republicans are attempting to do -- passing the bill and then selling it to a skeptical public -- amounts to a trapeze act with no net. They need to execute a series of flips and catches -- doing so while fully aware that the slightest slip or snafu likely means their hopes of holding the House (and maybe even the Senate) hinge on perfect execution.

It speaks to the desperation Republicans feel in advance of the 2018 midterms to do something -- anything -- big that they are willing to take such a giant risk. Here we go!