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

Trump endorses Ken Paxton in Texas Senate runoff, attacks opponent, and pushes voter ID and election security agenda ahead of Tuesday vote.

Texans are choosing a Republican nominee for U.S. Senate. The election brings to a close a bitter and expensive primary.

Cornyn led the March primary with 42% of the vote, narrowly ahead of Paxton’s 40.5%, sending both to a runoff.