Alabama's Roy Moore would be the most extreme senator — with huge consequences for Congress

Senate Majority Leader Mitch McConnell and his allies in the Republican establishment have spent four months and more than $10 million trying to defeat a fanatically religious conservative outsider running to fill the seat once held by Attorney General Jeff Sessions.

On Tuesday, that outsider — former Judge Roy Moore — will face off against incumbent Sen. Luther Strange, who has been backed by Senate leadership and President Trump, in the Alabama Republican Senate primary runoff. (Polls in Alabama close at 8 pm on Tuesday. You can view live returns here.)

@mjbeckel: ~$20 million has been invested into #ALSEN race, with "Team Strange" outspending "Team Moore" ~7-to-1 http://bit.ly/2yhJNvI #alpolitics

Moore believes in the supremacy of God's law over man's, and thinks, among other things, that Sharia law has already been implemented in some US cities and that the Constitution forbids Muslims from serving in Congress. He has tried to explicitly turn the GOP's Alabama Senate primary into a referendum on McConnell's leadership.

More from Vox:
Senate Republicans tweak Graham-Cassidy in latest bid to win votes
Report: Jared Kushner used private email for White House business
In apparent rebuke to Trump, NFL players kneel during national anthem

If Moore wins despite the national GOP's all-out attack — and the latest polls have him up by 8 points — then McConnell will not just have wasted a ton of money. He'll also have a new and remarkably powerful antagonist, one who will arrive in Washington owing the majority leader nothing.

"If you're McConnell, you're just peeing your pants over the prospect of a Moore win," said Jim Manley, who served as a top aide to former Senate Majority Leader Harry Reid. "It'd be like adding a mini thermonuclear weapon in the Republican caucus — with very dangerous consequences for those trying to reach compromise."

Strange has tried embracing Trump, who remains wildly popular in Alabama, as closely as possible — but that strategy may not be enough. The winner of the runoff still faces a general election against Democratic candidate Doug Jones in December, though Republicans hold a massive numeric advantage in the state, so the winner of the GOP runoff is all but guaranteed to be in the Senate.

Republicans in Washington may be beginning to reckon with the prospect of Sen. Roy Moore. Observers of the Senate say a Moore victory could reshape the Senate's equilibrium — perhaps by giving Democrats greater leverage for working with McConnell, but more likely by simply increasing the body's dysfunction and inability to compromise, and by giving a national platform to a judge whose political beliefs were once relegated to the far-right fringe of conservatism in Alabama.

To understand how Moore could upend the balance of the Senate, it's vital to understand his ideology — and why it puts him far afield from even the most conservative Republican currently in the Senate.

In particular, experts note that Moore's goal isn't merely for the government to carve out a space for free religious exercise, as many conservatives demand; instead, he argues that Christian principles — or, more accurately, his interpretation of Christian principles — should provide the foundation for, and even supersede, the laws of men.

"Moore's ideology is an express belief that God's law and his interpretation of God's law stand on top of man's law," said David Dinielli, deputy director of the Southern Poverty Law Center, who has tracked Moore's career for years. "It's an ideology that would allow those who think they know the unknowable and the mystic to impose their beliefs on everyone else."

This conviction resulted in the two high-profile national stories that gave Moore the name recognition now powering his Senate run. (Moore came in first in the first round of the GOP primary ahead of Tuesday's runoff.) The first was his decision to install a monument to the Ten Commandments at his courthouse. Despite direct orders from a federal judge, Moore then refused to remove the monument or to cease holding a prayer session in his courtroom, leading to his suspension.

"The Judeo-Christian God reigned over both the church and the state in this country, and [...] both owed allegiance to that God," he said at the time.

Moore was suspended again in 2015 after refusing to issue marriage licenses to same-sex couples. "Moore has ... encouraged lawlessness by attempting to assemble a virtual army of state officials and judges to oppose the federal judiciary and its 'tyranny,'" the SPLC wroteat the time.

In a 2006 column arguing that Muslim American Rep. Keith Ellison should not seated by Congress, Moore argued that the Constitution is founded on specifically Christian principles, and that anyone whose beliefs fall outside Christian principles by definition fall outside those of the Constitution as well.

"The Islamic faith rejects our God and believes that the state must mandate the worship of its own god, Allah," Moore wrote of Ellison. "Islamic law is simply incompatible with our law."

If Moore were running for a seat in the House, he'd join a coterie of conservatives in the Freedom Caucus that is already deeply right-wing. And his influence would be diluted as just one of 435 in a body where individual members have little choice but to follow the agenda put forward by leadership.

But as a senator, Moore would have much more power — both because each member of the Senate has far more leverage and authority than the average House member and because he'd have a greater platform to spread his views.

"One senator can really gum up the works," said Alan Abramowitz, a political scientist at Emory University. "The Senate rules give individual senators ways to throw a monkey wrench into the Senate if they choose to do so."

Abramowitz stresses that there are limits for how much damage Moore can do. Despite rules that grant individual senators vast powers — like unilaterally blocking judicial appointments or preventing bills from coming to the floor — the Senate can ultimately rewrite its rules with 51 votes to limit Moore's influence. So his ability to pass legislation that reflects his worldview will likely be sharply circumscribed.

"If he thinks he'll come in and start moving bills that will force the Ten Commandments to be hung outside of Sen. Sanders's office, he'll be sorely mistaken. He's hamstrung on the legislative front," said Manley, the former Reid aide. "The other senators will make sure he doesn't stray too far from the customs and norms of the Senate."

Moreover, there's a chance that having McConnell lose a safe vote redounds to Democrats' benefit. "If you have a few more extreme Republicans in the Senate like Moore going off the reservation and not supporting compromise, it means McConnell needs more Democrats to get things done," said Bruce Oppenheimer, a congressional scholar at Vanderbilt University. "If there are people who are totally uncompromising, you have to look elsewhere."

Still, Moore can make the body more conservative in a number of ways. He'll likely shift the center of gravity in the caucus to the right, giving the existing right-wing hardliners — Sens. Rand Paul (KY), Ted Cruz (TX), and Mike Lee (UT) — an additional vote to pull the party in their direction. "I can see him functioning as a quasi-Rand Paul, but perhaps more extreme," added Allen Linken, a political scientist at the University of Alabama.

Beyond the ability to torment McConnell's whip count, a Senate seat would also give Moore the capacity to widen the parameters of the policy debate in Washington in new directions.

For instance, virtually no senator seems interested in challenging the idea that the Constitution gives the federal government broad power under Article I, Section VIII, to do things that are not specifically identified as within the government's purview. After all, that precedent stems back to a Supreme Court case decided in 1819.

Not Moore. "He definitely has a different interpretation of federal unenumerated powers," Linken said. "I think he'll agree that Congress [can] spend money on certain implied powers, but it's definitely not what we're used to seeing."

That doesn't mean he'll be able to close the IRS in his first term; it does mean he'll be able to give these right-wing ideas far greater circulation. Already, Steve Bannon's Breitbart has waged a war against Strange and thrown itself behind Moore's campaign.

"On these cultural issues, Moore is going to horrify," Abramowitz said. "But I could see him getting a ton of media attention — he's a colorful character and very divisive, and that means ratings."

That could translate into a lot of useless hot air. Or it could allow Moore to use right-wing media to convert many more Americans to the belief that the federal government should have far less power than even Cruz and Paul believe.

But how far Moore would take the office depends on his ability to win on Tuesday. If he beats Strange, we could be about to find out exactly what a senator like Moore can do.

"He's going to be doing a lot of grandstanding, a lot of press conferences and going outside the formality of the Senate," Linken predicts, noting that Moore made a show of riding his horse, Sassy, to the polls on election day — "like an 1870s politician."

Commentary by Jeff Stein, Congressional reporter at Vox. Follow him on Twitter @JStein_Vox.

For more insight from CNBC contributors, follow @CNBCopinion on Twitter.