Donald Trump’s performance the past month — the countless controversies and continual taunts of the GOP establishment — is dramatically narrowing his options for vice president.

With the Republican convention a month away and Trump approaching a critical decision on his No. 2, each week crosses more names off the list. Trump has bashed star Republican Gov. Susana Martinez of New Mexico, and ignored the advice of senators like Bob Corker, who might have brought valuable foreign policy and congressional experience to the ticket. Sen. Marco Rubio has ruled out the post (even as he reconsiders running for reelection), while South Carolina Gov. Nikki Haley and Iowa Sen. Joni Ernst — both well regarded GOP figures who might improve Trump’s dismal standing among women and minorities — have all but done the same.

And John Kasich, who might have helped Trump in must-win Ohio and heal wounds with the party establishment, can’t even bring himself to support the presumptive nominee.

“It’s not going to make it easier” to select a running mate, Sen. John Thune (R-S.D.) said of Trump’s recent behavior. The Senate’s No. 3 Republican, Thune himself has been mentioned as a potential running mate. “There are probably some good options for him. The question is: Are there people for whom he is a good option?”