Ben Sasse, a Republican Senator from Nebraska, is under fire for grinning and not initially speaking up when Bill Maher used a racial slur on HBO.

Sasse was Maher’s guest at the time the comedian used the n-word. Specifically, Maher called himself a “house n**ga” in a conversation with Sasse. Sasse was on the show to promote his book, The Vanishing American Adult.

Now, Sasse has responded to the criticism by posting a multi-part statement to Twitter in which he claims he cringed when Maher used the slur and wishes he’d spoken out against it at the time.

You can watch video of the Sasse-Maher exchange here. Some on Twitter say it’s unfair that others are blaming Sasse for something Maher said, however.

Here’s what Sasse wrote later on Twitter:

“Am walking off a redeye from LAX. 3 reflections on @billmaher 1. I’m a 1st Amendment absolutist. Comedians get latitude to cross hard lines.”

“But free speech comes with a responsibility to speak up when folks use that word. Me just cringing last night wasn’t good enough.”

“Here’s what I wish I’d been quick enough to say in the moment: “Hold up, why would you think it’s OK to use that word?..”

“…The history of the n-word is an attack on universal human dignity. It’s therefore an attack on the American Creed. Don’t use it.”

Here’s another screenshot from the moments after Maher used the slur.

Sasse’s website calls him “one of the leading conservative voices in the Senate.” His website touts how he campaigned in a rickety bus. “He was elected in a 2014 landslide, winning each of Nebraska’s 93 counties, and securing the second-largest margin for a new senator in the history of the state. Living off of a rickety old campaign bus, he and his family campaigned tirelessly on a common-sense platform of restoring the Constitution to its rightful place and encouraging a more constructive politics where every public official works to make the American Dream achievable for every family.”

Sasse has a PHD in American History from Yale University and wrestled in college, his website says. He was the president of a Lutheran college when elected to the U.S. Senate. Sasse is a never Trump Republican.

Here’s the transcript of his conversation with Maher that ended in Maher using the racial slur. Maher’s slur has sparked outrage, with some on Twitter comparing the comedian to Kathy Griffin. The audience applauded after Maher used the slur, and Sasse smiled and didn’t say anything at the time.

Sasse was on Real Time With Bill Maher on June 2.

“Adults dress up for Halloween, they don’t do that in Nebraska?” Maher asked.

“It’s frowned upon,” Sasse replied. “We don’t do that quite as much.”

“I gotta get to Nebraska more,” Maher said.

“We’d love to have you work in the fields with us,” said Sasse.

“Work in the fields?” responded Maher. “You said it. I’m a house n**ga.” Maher held up his hands as he uttered the slur, smiling, and the audience applauded. Sasse grinned in response.

Sasse was previously known for speaking out against racism in the Republican Party. He once said he would leave the party if it became the party of David Duke.

“I signed up for the party of Abraham Lincoln, not the party of David Duke, Donald Trump,” Sasse said, according to the Hill, “linking the white nationalist with Trump’s White House run.”

“I hope it happens over the course of the next 30 to 60 days that the Republican Party again becomes the party of Abraham Lincoln, limited government and great human potential. I want to celebrate what’s great about America in the Republican Party, but if the Republican Party becomes the party of David Duke, Donald Trump, I’m out,” Sasse said, the Hill reported.