Early voting for the primary runoff election begins Monday. Unlike the primary election, the runoff is always a head-to-head matchup. For the candidates, winning hinges more on turning out more of your original voters than it does on winning over others’ voters (or non-voters).Nine incumbent legislators – eight Republicans and one Democrat – were forced into runoffs in their efforts to keep their seats. They will need to buck history to do so.Since 1996, just 10 of 38 incumbent legislators forced into runoffs prevailed (26%), including a history-bucking three out of four in 2022. All 10 of those victorious incumbents finished in first place in their respective primary elections. Only two of the nine incumbents forced into runoffs this year finished first: Reps. Stephanie Klick and Gary VanDeaver.The other seven, including Speaker Dade Phelan, finished in second place in their respective primaries. No incumbent legislator who finished in second place in their primary has won a runoff since 1992, when Sen. John Whitmire eked out a 52%-48% victory after finishing second to Roman Martinez by 2.7 percentage points in the primary.Speaker Phelan risks becoming the first sitting House Speaker to be ousted in a primary or primary runoff since Speaker Rayford Price lost the 1972 Democratic runoff to Rep. Fred Head, a member of the “Dirty Thirty” who had been paired the Speaker in redistricting. Like Phelan, Price finished second in the three-way primary election. (Incidentally, then-former Speaker Gus Mutscher, who had already resigned the speakership following a bribery conspiracy conviction, lost his Democratic runoff to Latham Boone III).These defeats arose from strong voter unrest in the aftermath of the Sharpstown Scandal, which resulted in the outright defeat of 14 House incumbents in the primary. Another 16 House incumbents were forced into runoffs. Ten were defeated. An Associated Press article from June 5, 1972, noted “As the sun rose Sunday, all the politicians even remotely connected with the Sharpstown scandals were in eclipse.”One stunning aspect of 2024’s tumultuous Republican primary and runoff is that there is no such scandal. Instead, the carnage has been largely driven by voters’ reactions to two votes: impeaching Attorney General Paxton toward the end of the regular session and rejecting school choice (or vouchers, depending on your perspective) in a recent special session.A second stunning aspect of the 2024 primary season is the active involvement of the governor to oust incumbents of his own party. In 1972, then-Gov. Preston Smith had to focus on his own re-election (He lost.). This year, Gov. Abbott is not on the ballot, allowing him to use his formidable war chest to influence primary elections. Abbott spent around $6M to aid Republican primary challengers before the March primary. Early next week, we should know how much more Abbott has spent to defeat incumbents.But there is one other similarity between 1972 and 2024. In both elections, the incumbents tended to be, or be portrayed as, centrists as the faced challenges from staunch liberals (1972) or the more staunchly conservative Republicans (2024). Each election captures a decisive left- (1972) or right-ward (2024) movement of primary voters.The Democratic primary electorate remained much more liberal even as the overall electorate grew more conservative. The last Democratic presidential nominee to win Texas was Jimmy Carter in 1976. Two years later, Bill Clements became the first Republican governor since Reconstruction. No Democrat has won statewide since 1994.As they say in any investment fund ad, past performance does not imply future returns. One could read too much into the historical similarities, and trajectories, arising from a centrist purge in a party’s primary election. But historical patterns are patterns for a reason. In the micro-level, we will see if longtime trends hold with respect to incumbent legislators forced into runoffs. The macro-level will take longer – it always does.Sharpstown proved a seminal moment in Texas politics. Will the ultimately unsuccessful effort to remove Paxton from office prove to be another?