The primary challengers just keep on coming, with the additions this week of Minuteman Founder Chris Simcox running against Sen. John McCainJohn Sidney McCainColbert mocks Gaetz after Trump denies he asked for a pardon Five reasons why US faces chronic crisis at border Meghan McCain calls on Gaetz to resign MORE (R-Ariz.), Memphis Mayor Willie Herenton possibly challenging Rep. Steve Cohen (D-Tenn.) and Lackawanna County Commissioner Corey O'Brien lining up a run against Rep. Paul Kanjorski (D-Pa.).

Four incumbents lost in primaries last year and several others came close or were held to 50 percent or lower, so blood is in the water. But some of the most serious primary challenges to emerge so far have actually come against members who haven't exactly been primary-prone - people like Kanjorski and Reps. Allen Boyd (D-Fla.) and Sander Levin (D-Mich.).

So who else is at risk of a serious intra-party challenge? Here's a scorecard:

-Already taking shape: Cohen, Kanjorski, Boyd, Levin, and Reps. Dan Burton (R-Ind.), Henry Brown (R-S.C.), Bob Inglis (R-S.C.)

-Ripe: Reps. Phil Roe (R-Tenn.), Don YoungDonald (Don) Edwin YoungButtigieg charms Washington with his accessibility Pro-union bill passes House, setting up lobbying battle in Senate Lobbyists eager for return to earmarks MORE (R-Alaska), Carolyn Kilpatrick (D-Mich.), Laura Richardson (D-Calif.), Jane Harman (D-Calif.)

Roe and Young both face potential rematches in races they won narrowly. Kilpatrick took a measly 39 percent in 2008, and Richardson's financial and real estate problems didn't come to light until it was too late to primary her in 2008. Harman is a special case: she has never been a friend of liberals or House Speaker Nancy Pelosi (D-Calif.), she yielded 38 percent to an poorly funded primary opponent in 2006, and now she has to deal with some serious accusations about influence-peddling and AIPAC.

-Worth keeping an eye on: Reps. Ed Towns (D-N.Y.), Doug Lamborn (R-Colo.), Dennis Kucinich (D-Ohio), Pete Visclosky (D-Ind.)

Towns, Lamborn and Kucinich have all taken 50 percent or less in recent primaries, but Towns's and Lamborn's opponents couldn't get much traction last year, and Kucinich probably isn't as vulnerable with his fleeting presidential campaigns further in the rearview. Visclosky could be in trouble thanks to the PMA Group scandal, as he is a top recipient of its money and a top PMA earmarker. He recently asked permission to use campaign funds for his legal fees - never a good sign.

-Sliver of a chance: Reps. Jared Polis (D-Colo.), Jason ChaffetzJason ChaffetzCongress's latest hacking investigation should model its most recent Fox News Audio expands stable of podcasts by adding five new shows The myth of the conservative bestseller MORE (R-Utah), John FlemingJohn Calvin FlemingTrump wants Congress to delay Census deadlines amid pandemic Meadows sets up coronavirus hotline for members of Congress The Hill's Morning Report - Iran strikes US bases in Iraq; Trump to speak today MORE (R-La.), Blaine Luetkemeyer (R-Mo.), Lynn Jenkins (R-Kan.), Joe WilsonAddison (Joe) Graves WilsonBiden faces deadline pressure on Iran deal Top Republican congressional aide resigns, rips GOP lawmakers who objected to Biden win READ: The Republicans who voted to challenge election results MORE (R-S.C.)

The first five are freshmen coming off tough primaries where feelings could still be hard, though its difficult to see former Rep. Jim Ryun (R-Kan.) trying again versus Jenkins; Wilson was weak in the general election, and there appears to be something in the water in the Palmetto State, with free-for-alls forming for all of the other three GOP-held House seats.

-Have proved themselves and should rest easy: Reps. Dan Lipinski (D-Ill.), Andre Carson (D-Ind.), John BarrowJohn Jenkins BarrowOn The Trail: The political losers of 2020 Republican wins Georgia secretary of state runoff to replace Kemp The most important runoff election is one you probably never heard of MORE (D-Ga.), Ralph HallRalph Moody HallUpton becomes first member of Congress to vote to impeach two presidents John Ratcliffe is the right choice for director of national intelligence — and for America Rising star Ratcliffe faces battle to become Trump's intel chief MORE (R-Texas), Ron Paul (R-Texas)

Lipinski and Carson both sailed in tough primaries last year, and it's doubtful that any serious opposition shows up to face Barrow or either of the Texans, who turned away nominal opponents in 2008.

-Aaron Blake