If, as expected, Mitt Romney wins his race for a Senate seat from Utah he may become the most powerful man in the United States Senate. As many of us remember, Romney, former Governor of Massachusetts, ran for president in 2012 and lost to Barack Obama. It wasn’t one of those totally humiliating losses—the map did not turn blue—but we assumed Mitt Romney would fade into history.

Well, maybe not.

Here’s how. Just a few months ago, conventional wisdom was that while the Democrats had a good chance of taking control of the House of Representatives, the Senate was out of reach. In 2018 there will be at least 35 Senate seats up—of which 26 are held by Democrats. Democrats need a net gain of 2 seats to take control of the Senate. In an ordinary year this would be tough for two reasons. One is that incumbents usually win, and secondly, 10 of those Democratic senators represent states that went for Trump in 2016—so a somewhat popular president might be able to use his clout to win a Senate seat back from the Democrats. But this is no ordinary year as poll after poll and special election after special election indicate a “blue wave” for Democrats.

Recently, a spate of new polling has opened up the possibility that Democrats could win one or more seats in heavily Republican states. In Tennessee, several recent polls have former Democratic Governor Phil Bredesen leading Republican Rep. Marsha Blackburn. In Arizona, in the race to replace retiring Republican Senator Jeff Flake, Democratic Rep. Kyrsten Sinema is polling ahead of all three possible Republican nominees. (The Republican primary is in August.) And, to the surprise of many, Democratic Rep. Beto O’Rourke is polling close to incumbent Republican Ted Cruz in the very red state of Texas.

Romney is running for Senate from Utah in the seat Orin Hatch has held since before Jimmy Carter was inaugurated as president. Romney’s campaign faced an unexpected bump in the road when he came in second in the state convention and will thus have to run in a primary—a situation that often benefits the better-funded candidate. For instance, Governor Gary Herbert lost the convention by 10 points in 2016 and won the primary in a landslide. Assuming Romney wins the June Republican primary he will certainly win the general election seat in this very Republican state.

The seat will remain Republican-held for President Trump come January of 2019, but this one could very well turn out to be the swing vote in the Senate. If Democrats pick up one seat, not two, the Senate will be tied and Trump will have to continue to rely on Vice President Pence to cast tie-breaking votes, unless other Republicans defect. In that scenario Romney, a frequent critic of President Trump’s, could easily upset the balance of power.

The reason? Republican Senator Romney will have what no other Republican Senator currently has, a Republican constituency that does not like President Trump. Trump came in third in the Republican primary in Utah in 2016 and in the general election a large number of voters voted for the independent and Mormon conservative Evan McMullin, rather than pull the lever for Trump or Hillary. For comparison, in 2016 Donald Trump won about 45 percent of the general election vote in Utah; in 2012, Romney won about 73 percent of the presidential vote there. Mormon voters, who make up the majority of voters in Utah, are perhaps the only conservative religious bloc in the country who are bothered by President Trump’s many infidelities and dubious business practices—Trump’s approval among Mormons trails behind white evangelicals by 14 points.

Thus, as Senator from Utah, Romney would have fewer electoral constraints on him to support the president than just about any other senator from a solidly red state. And he has already made it perfectly clear that he considers Trump a “con man,” an “imposter,” a “phony, a fraud.” He has criticized Trump for his business failures and for his sexual indiscretions. He will not commit to supporting him in 2020. On matters of Republican orthodoxy, like lowering taxes, Romney would vote like other Republicans, after all, Senators Jeff Flake (R-Ariz.) and Bob Corker (R-Tenn.)—also vocal Trump critics—voted for the tax bill. But it is the other votes Trump should fear, such as a vote to protect Bob Mueller’s job and keep the Russia investigation going.

If the blue wave is so big that it produces a Democratic Senate in 2019, Romney will be the junior senator from Utah in the minority party. But the more likely outcome is very close Republican control of the Senate. In that case Mitt Romney, the man who failed to become the king, may very well become the kingmaker.