Ken Paxton, the Trump-endorsed and MAGA-backed insurgent, ousted Sen. John Cornyn in a runoff Tuesday, becoming the second primary challenger to knock out an incumbent Republican senator in less than two weeks in a raw display of President Donald Trump’s powerful hold on the party base.The contest was the most expensive primary in American history -- and Paxton prevailed despite being outspent on advertising by pro-Cornyn forces by roughly $80 million.Now, Republicans are bracing for a potentially competitive general election in Texas, where Democrats have not won statewide in a generation. Democratic donors nationwide have swooned for their nominee, James...