Washington (CNN) -- It's one of the busiest days in this year's primary calendar. Six states from coast to coast hold primaries on Tuesday, and again anti-establishment candidates face long odds in high-profile Republican showdowns. Since its birth in 2009, the tea party has had a number of primary successes, with victorious challenges from the right producing major headlines for the movement. But they've also given the party plenty of headaches and hurt its chances of winning back the Senate, effectively costing the GOP five winnable elections over the last two cycles. This year, the establishment learned to fight back, and so far has had the upper hand in most contests against tea party-backed challengers. Here are five key showdowns to watch how they play out on Tuesday.
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Senate Minority Leader Mitch McConnell faces tea party challenge
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Incumbent Idaho congressman is expected to fend off tea party challenge, too
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Tea party candidates might be splitting the vote in Georgia Senate primary
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Pennsylvania governor's race is a race to the left among Democrats
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