President Donald Trump's tightening grip on his party could make it harder to win in the November midterms, when Republicans face a broader electorate that has soured on the president's second term and the economy.

President Donald Trump abandoning Sen. John Cornyn destabilizes the White House's already-rocky relationship with Senate Republicans.

Donald Trump's power over Republican voters faces another test Tuesday in Texas, where veteran Senator John Cornyn is fighting long odds after the president endorsed…