Lauren Arthur is the 42nd Democrat this cycle to win a red seat in a special election.

On Tuesday night, as major primaries all across the nation were decided, yet another special election was held, this time for a vacant GOP-held seat in Missouri. Well, it was GOP-held — until the seat flipped blue on Tuesday.

Democratic candidate Lauren Arthur — a Missouri state representative who previously served as an inner-city middle school teacher, worked with Teach For America, and sits on the Children’s Trust Fund board — prevailed in her contest against Republican state representative and local attorney Kevin Corlew for Missouri’s 17th Senate District.

Arthur ran on a platform including education investment, Medicaid expansion, worker rights, and campaign finance reform. Corlew backed the GOP tax scam, and opposed abortion rights and gun control.

This victory marks the 42nd state legislative seat that Democrats have flipped blue since Trump’s election, in addition to the open Senate and House seat Democrats picked up.

Missouri’s 17th District includes the cities of Liberty and Gladstone, directly northeast of Kansas City. The seat was vacated when GOP state Sen. Ryan Silvey was appointed to the Public Service Commission. Its voters chose Trump by 4 points, and Silvey by 23 points. Arthur took the seat by 20 points — a truly colossal swing toward Democrats.

The GOP may have been injured by the fallout from Gov. Eric Greitens, who resigned in disgrace last week amid allegations he stole computer data from a charity, and sexually assaulted and blackmailed his former hairdresser.

Teachers are also ascendant in political power this year, having successfully forced lawmakers in red states to make new investments in public education. They are now running for office in droves.

Arthur’s massive win in Missouri is yet another sign of the sustained, progressive electoral might building to take on the GOP this fall. And it’s also another reason for Republicans to be worried.