John Cornyn

In the final week of what may be his last campaign, Senator John Cornyn of Texas posed for photos in a mostly empty oak grove in Austin and doled out hugs at a San Antonio senior living center.

By the time he got to Houston on Thursday, he assured his supporters that he was “running through the tape.” Updates from the campaign were tagged “stillwithCornyn” on social media.

It could be interpreted as a warning sign that Mr. Cornyn had to tell supporters that he would keep campaigning until the primary runoff ends on Tuesday.

Such assurances became necessary last week after President Trump threw his considerable Republican primary weight behind Mr. Cornyn’s opponent, Ken Paxton, the MAGA-aligned Texas attorney general.

The last-minute endorsement shook Mr. Cornyn’s campaign and made what was already a tough re-election fight into a much more daunting battle.

Mr. Cornyn’s supporters began to seriously consider the possibility that the man they had cherished for his steadfastness and decency in over four decades in public life might very well lose.

Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.

Thank you for your patience while we verify access.

Already a subscriber? Log in.

Want all of The Times? Subscribe.