Roberts is expected to win, but then again, so was Lugar. And the Kansas contest has tightened down the home stretch, according to polls, making Tuesday’s returns well worth tuning in for.

If Roberts wins and Sen. Lamar Alexander fends off Joe Carr in Tennessee on Thursday, this will be the first cycle since 2008 in which no incumbent senator loses in a primary.

Michigan, Missouri and Washington also have significant House primaries on Tuesday.

Top national Republicans privately concede that they are worried about an upset in Kansas, especially if fewer than 300,000 people turn out to vote during the height of vacation season. They fret that Roberts has not run an aggressive enough campaign, and that the X-ray story broke too soon in the campaign, allowing Wolf time to recover.