The month of May brings the first Senate primaries of the year. Ohio voted first, followed by a near weekly stream of contests that will shape the midterm battle for control of the chamber. By the end of the month, the general election matchups in almost half of this year's most competitive races will be set.
Republicans only need a net gain of one seat this fall to win the Senate, and so far, much of the intrigue about the May primaries has been on the GOP side. Former President Donald Trump has endorsed in all four Senate contests on the ballot in May that are expected to be competitive in the fall -- Ohio, where his chosen candidate won on May 3, North Carolina (May 17), Pennsylvania (May 17) and Georgia (May 24). Those primaries have cemented his hold on the party because of the way so many GOP candidates, even those without his endorsement, have tried to appeal to him -- in some cases, twisting themselves into almost unrecognizable versions of their former selves.
Trump's support has played differently in each state. In Ohio, it helped "Hillbilly Elegy" author J.D. Vance win the primary, likely blunting the biggest attack attack on him -- the candidate's past criticism of Trump.
The former President's backing of Mehmet Oz in Pennsylvania hasn't had as clear of an immediate impact, especially considering voters may have already associated the two celebrity Republicans together. And the millions in negative advertising spent attacking Oz or former hedge fund executive David McCormick seems to have opened a lane for conservative commentator Kathy Barnette. One Trump adviser said the former President is feeling "nervous about Oz's prospects," CNN's Gabby Orr reported, especially after his endorsed candidate didn't win Nebraska's gubernatorial primary on May 10.
Trump weighed in on the North Carolina primary nearly a year ago, but his backing of US Rep. Ted Budd didn't clear the GOP field. In Georgia, however, his commitment to Herschel Walker likely kept other top-name Republicans out of the race, leaving the former NFL star with what's expected to be a relatively easy path to the Republican nomination at the end of the month.
Democrats argue that this month's messy and expensive GOP primaries will leave Republican nominees bruised heading into the general election. (Democrats also have a crowded primary in Pennsylvania, but it hasn't attracted anywhere near the level of spending or vitriol as the GOP contest.)
After watching Republican candidates run to the right to try to win their party nods, Democrats are hoping to make general election matchups a contrast in candidates. But that gets harder to do if the national environment continues to work against the party. President Joe Biden's approval rating was at 41%, with 59% disapproving, according to CNN's latest poll, conducted by SSRS from April 28-May 1. Democrats know Republicans will tie them to him, which is one reason why a number of them have broken with the White House on lifting Title 42, a Trump-era public health authority that allows border authorities to turn migrants back to Mexico or their home countries.
Senate contests are increasingly becoming nationalized affairs, so while candidate quality does matter (see No. 10 on this list), Democrats face a tough challenge in holding their razor-thin Senate majority, regardless of which Republicans emerge from these May primaries.
CNN's ranking of the Senate seats most likely to flip sees a few changes this month, all in Republicans' favor. But the states holding May primaries remain in the same positions this month. The ranking is based on CNN's reporting and fundraising and advertising data, as well as historical data about how states and candidates have performed.