MS NOW's Jonathan Capehart on Sunday painted a vivid picture of one anxious Republican senator sweating out President Donald Trump's primary endorsement decision — and warned the GOP that Trump's habit of meddling in primaries could backfire in swingier states.Discussing Saturday's stunning Louisiana primary defeat of Sen. Bill Cassidy, one of the seven Republicans who voted to impeach Trump, Capehart turned his attention to Texas, where Sen. John Cornyn is locked in a primary fight with controversial Attorney General Ken Paxton."Senator John Cornyn is probably looking at what happened last night in Louisiana and is probably chewing his fingers down to a nub because he is still waiting for President Trump to endorse him over Ken Paxton in the Texas Senate primary," Capehart said on MS NOW.The host pointed to Cornyn's increasingly desperate attempts to win Trump's favor, noting that the longtime Texas senator floated this week the idea of renaming a highway "the President Donald J. Trump Highway.""He's doing everything he can to get the president's endorsement," Capehart said.The panel warned that while Trump's primary picks tend to survive in deep-red states like Louisiana, GOP strategists are increasingly nervous about him "dilly dallying" in purpler states where candidate quality matters in the general election.In his Saturday concession, Cassidy took thinly veiled shots at the president, saying, "When you participate in democracy, sometimes it doesn't turn out the way you want it to, but you don't pout. You don't whine. You don't claim the election was stolen."