COLUMBUS — Ohio Gov. John Kasich says he still can not endorse his party’s nominee for president.

In an appearance on MSNBC’s “Morning Joe” on Thursday, host Joe Scarborough asked the Ohio Republican for his response to a retweet from real estate tycoon and reality TV star Donald Trump, telling Republicans to “get on board” or leave the party.

“It’s painful,” Kasich replied. “I’m not making any final decision yet, but at this point I just can’t do it.”

Kasich, who ended his quest for the Republican nomination in May, has been critical of Trump’s response to the mass shooting at a gay club in Orlando, Florida, by a man who proclaimed himself affiliated with ISIS.

As news reports of the attack were coming in, Trump took to Twitter to thank supporters who he said “congratulated” him for being right about a proposed ban on immigration from Muslim countries.

Later in the week, Trump drew criticism for additional comments that many observers, including the Washington Post, said insinuated that President Barack Obama had something to do with the attack and invoked conspiracy theories that the president is a Muslim.

In an interview with Yahoo News, Kasich addressed Trump’s comments.

“Terrible. It’s not the way you operate as a leader. ‘I told you so”? What’s the magic of that?” Kasich said. “And then, to somehow insinuate that the president of the United States accepts this or condones this, it’s just outrageous.”

Trump is set to be nominated by his party at the Republican National Convention in Cleveland in July. While Kasich says he will still attend the convention, he has not made clear what his role in the event will be.

Democrats have sought to make Trump an issue for Republican candidates in the general election.

The campaign of Democratic former Gov. Ted Strickland, who is challenging U.S. Sen. Rob Portman, R-Ohio, in the fall, used Kasich’s comments as an opportunity to criticize their opponent, who has endorsed Trump.

“Governor Kasich’s refusal to back Donald Trump is a thunderous reminder that Senator Portman is continuing to endorse one of the most toxic presidential nominees in modern history — and that Portman’s spineless blend of political calculation, fear, and weak leadership represents exactly what Ohioans hate about Washington insiders,” the Strickland campaign said in a statement on Thursday.