Last week, Republicans in the Montana state Senate voted to adopt a top-two primary system1 — but only for U.S. Senate races, and only for the 2024 election. Republicans say the bill is a “test run” to see if a top-two primary is a good idea, but Democrats say it is an attempt to defeat Democratic Sen. Jon Tester, who is running for reelection in 2024 and has frustrated Republicans with his ability to win elections in this red state. But if that’s Republicans’ true motivation, they have a problem: Their strategy probably won’t work.
If the bill becomes law, it would virtually guarantee that the 2024 general election would be a head-to-head contest between Tester and a Republican. No third-party candidates would be allowed,2 a coup for Republicans who believe that Tester is only in the Senate today because a Libertarian candidate siphoned off Republican votes. Libertarian voters are generally considered to be more conservative than liberal. And in two of Tester’s previous three elections, the Republican and Libertarian candidates combined for more votes than Tester.
But here’s the thing: You can’t just assume that every Libertarian voter would have voted Republican if the Libertarian candidate hadn’t been on the ballot; elections don’t work like that. In fact, by our reckoning, Tester probably still would have won each of his previous elections even without a Libertarian on the ballot.
The closest call would’ve been in Tester’s first victory, in 2006. That year, Tester defeated Republican then-Sen. Conrad Burns by 3,562 votes, while Libertarian Stan Jones took 10,377 votes. Mathematically, Burns could have won if Jones had not been in the race and Jones’s supporters had broken for Burns by a margin of at least 67 percent to 34 percent.
However, that assumes that all those Libertarians still would have voted if Jones hadn’t been on the ballot. In other elections, a majority of third-party voters have told exit pollsters that they wouldn’t have voted at all if their only choices had been a Democrat and a Republican. And Jones was critical of Democrats and Republicans, so many of his votes could’ve been protest votes cast by people who couldn’t stomach either of the major candidates.
In the hypothetical scenario where Jones didn’t run and some of his supporters stayed home, Burns would have needed to win an even larger share of Jones’s remaining voters in order to net 3,563 votes. Let’s dive into the math. If only 90 percent of Jones’s supporters had turned out (9,339 voters), Burns would have needed to win them 6,451 to 2,888 (69 percent to 31 percent). And if only 50 percent of Jones’s supporters had turned out (5,189 voters), Burns would have needed to win them 4,376 to 813 (84 percent to 16 percent).
If any significant share of Jones’s voters had stayed home, Burns would have needed to win the remainder by a punishing margin to defeat Tester. It wouldn’t have been impossible, but it would have been unlikely.
Next, let’s examine Tester’s first reelection campaign in 2012. Even though a liberal outside group spent $500,000 on ads calling Libertarian Dan Cox the race’s “real conservative” in an attempt to undermine GOP support, it’s doubtful that this threw the election to Tester. Tester defeated Republican then-Rep. Denny Rehberg by 18,072 votes as Cox received 31,892 votes. Therefore, if Cox hadn’t been on the ballot and every Cox supporter had still voted, Rehberg would have needed to win them by a landslide margin: at least 78 percent to 22 percent.
And if turnout among Cox supporters had been any lower than 57 percent, it would have been mathematically impossible for Rehberg to catch Tester using Cox voters, even if every single one voted for him.
Finally, we know that in 2018, a Libertarian candidate didn’t cost Republicans the election because Tester got a majority of the votes cast in the race that year. Even if GOP Rep. Matt Rosendale had gotten all of Libertarian Rick Breckenridge’s votes, it still would have been 3,368 votes shy of Tester’s total.
Whether Montana will adopt a top-two primary for its 2024 Senate race remains to be seen. The bill still needs the approval of the state House and Gov. Greg Gianforte before it can become law. But if it does, it clearly wouldn’t doom Tester’s campaign. He probably still would have won under such a system in 2006 and 2012. And the 2018 election shows he’s at least capable of winning an outright majority.
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But that doesn’t mean Republicans’ attempt to change the law is harmless to Democrats: It could make a difference if Tester’s 2024 race is decided by an even thinner margin than his three previous campaigns.
More importantly, this bill is part of a pattern from Montana Republicans to tilt the state’s electoral playing field in their favor. In 2021, they unsuccessfully proposed ending statewide elections for the state Supreme Court in favor of electing justices by district — districts that would be drawn by the Republican legislature. The same year, Republicans also changed the state’s voter-ID law so that a student ID from a Montana college would no longer suffice. And this isn’t the first time they’ve tried to switch to a top-two primary system to boot. So even if this attempt fails too, the threat to democratic norms likely won’t be over.
CORRECTION (April 10, 11:45 a.m.): A previous version of a table in this story incorrectly referred to the year in which Jon Tester defeated Conrad Burns and Stan Jones to win Montana's U.S. Senate race. It was 2006, not 2012.