(CNN) When Alabama voters go to the polls Tuesday to choose between Roy Moore and Doug Jones, they are, ostensibly, picking one out of 100 senators -- not to mention someone who will only serve until 2020 before having to run again.

But this Alabama special election matters a whole heck of a lot more than that. There are widespread implications that go well beyond the borders of Alabama and could influence not just the 2018 election but the broader images of the two political parties heading into 2020 and beyond.

The massively high stakes are why you see both President Donald Trump and former President Barack Obama -- as well as a number of Democrats who would like to take on Trump in 2020 -- getting involved in the race as it reaches its conclusion. Anyone who is anyone -- or wants to be anyone -- is making sure their voice is heard in Alabama right about now.

Below, a list of the very real stakes in tomorrow's special election.

1. Trump's policy agenda

Republicans have a narrow two-seat Senate majority. Given the vocal anti-Trump wing (John McCain, Jeff Flake, Bob Corker) and the number of moderate skeptics (Lisa Murkowski, Susan Collins) within the Republican Senate conference, it's already very, very difficult to get legislation passed. (See: Obamacare, repeal of.) If Jones managed to win -- and polling is all over the map on the race -- then Republicans would be down to a single-seat edge until next November.

For Trump priorities like building a wall along the Mexico border or entitlement reform, a one-seat advantage for Senate Republicans isn't enough. And if past is prologue, Democrats feel absolutely no pressure -- politically or otherwise -- to sign onto any Trump agenda item. Which means that even a single Republican opposing Trump forces Vice President Mike Pence to break a Senate tie. Two Republicans opposing a Trump priority and that priority is doomed.

2. The 2018 election

Every politician in Washington is watching to see what happens in Alabama. Every. Single. One. By any traditional political calculus, Moore should lose given the allegations of inappropriate sexual conduct with teenagers while in his 30s leveled against him. (Moore denies all the charges.) But we are in extraordinary political times. Trump, after all, won while dismissing accusations of sexual misconduct from multiple women during the 2016 campaign.

At issue for Republicans is whether the Trump base -- which views what the President says as gospel truth and believes the media is lying, at all times, for partisan purposes -- turns out to vote for Moore and whether that turnout is enough to put him over the top. Democrats, by contrast, are trying to figure out whether they can come close to approximating the African-American turnout during the two presidential races of Obama.

If Moore manages to win, expect the rising voices of criticism within the GOP to grow quieter -- for fear of Trump. If Moore loses, the opposite will be true: The floodgates of Trump criticism from within his own party are likely to break open.

3.The GOP brand

The idea of Sen. Roy Moore terrifies most Republicans who have to be on the ballot next year. That sentiment was summed up nicely by the ever-quotable Sen. Lindsey Graham on CNN on Monday:

"Roy Moore will be the gift that keeps on giving for Democrats and define the 2018 election, at least 2018, and to think you can elect Roy Moore without getting the baggage of Roy Moore is pretty naive."

While the immediate concern -- as Graham rightly notes -- is the 2018 election, the prospect of Moore in the Senate potentially has much longer tentacles. Democrats can -- and will -- portray Republicans as the party of Trump (more than a dozen women accusing him of sexual misconduct) and Moore (a series of allegations about inappropriate behavior toward teenage girls) at every chance they get.

Yes, both men have denied the allegations -- fully. But those denials -- particularly given the number and credibility of the accusers -- won't satisfy lots and lots of voters.

Democrats, sensing opportunity, have worked to purge alleged sexual harassers from their ranks with the resignations of Sen. Al Franken of Minnesota and Rep. John Conyers of Michigan in recent days. Such moves are clearly designed to regain the moral high ground when it comes to men behaving badly with women.

4. The #metoo movement

In the last week, the #metoo movement has come to Capitol Hill -- after becoming a driving cultural force in entertainment and media in the months since allegations about Harvey Weinstein's behavior went public.

Rumors are swirling -- in the wake of the planned resignations of Franken, Conyers and former Arizona Republican Rep. Trent Franks -- that more members of Congress may be swept up in all of this soon.

A Moore loss would suggest that the shift in the culture has come to politics -- even in a state as traditionally red as Alabama. A Moore win, on the other hand, might well serve as a sort of silencing mechanism for women in politics who are weighing whether or not to come forward with their own allegations of sexual misconduct. If Moore succeeds in spite of all of the women who have come forward, all telling very similar stories about how he approached them and what he wanted, there could well be a sense among women weighing whether to go public that it's simply not worth it given the potential fallout.

5. Donald John Trump

The President spent a few weeks playing coy about his support for Moore -- citing the fact that he was in Asia when all of this news broke. He is playing coy no longer. Not only has Trump endorsed the controversial former judge, but he held a de facto get out the vote rally for Moore on Friday night in Pensacola, Florida and has recorded robo-calls in the state for the Republican nominee.

For all of the White House's talk that they want to let Alabama voters decide on their senator, Trump has put a major thumb on the scale for Moore in the last 10 days. Which means Trump has skin in the game. Which means he has to own a loss by Moore -- if that happens. (You can be sure Trump will claim credit for pulling Moore over the line if the GOP nominee wins.)