President Trump talks to reporters on his way to board Marine One at the White House earlier this month. (Jabin Botsford/The Washington Post)

A Republican state lawmaker in Nebraska is calling out President Trump and his party for “enabling white supremacy” in the United States.

In a series of tweets written Sunday night in the wake of mass shootings in El Paso and Dayton, Ohio, that left 31 people dead, state Rep. John McCollister said it pained him to share that conclusion as a lifelong member of the Republican Party.

The Nebraska Republican Party responded late Monday that McCollister “should tell the truth and change his party registration.”

“I of course am not suggesting that all Republicans are white supremacists nor am I saying that the average Republican is even racist,” wrote McCollister, who represents an Omaha-area district. “What I am saying though is that the Republican Party is COMPLICIT to obvious racist and immoral activity inside our party.”

McCollister, who was first elected in 2014 and has been described as a moderate Republican, pulled no punches when discussing Trump, who has downplayed the threat of white nationalism in the country.

“We have a Republican president who continually stokes racist fears in his base,” he said in his tweets. “He calls certain countries ‘s---holes,’ tells women of color to ‘go back’ to where they came from and lies more than he tells the truth. We have Republican senators and representatives who look the other way and say nothing for fear that it will negatively affect their elections.”

“No more,” McCollister continued. “When the history books are written, I refuse to be someone who said nothing. The time is now for us Republicans to be honest with what is happening inside our party. We are better than this and I implore my Republican colleagues to stand up and do the right thing.”

In a statement, Ryan Hamilton, executive director of the Nebraska Republican Party, said McCollister should “re-register as a Democrat.”

“John McCollister has been telegraphing for years that he has little if nothing in common with the Republican voters in his district by consistently advocating for higher taxes, restrictions on Americans’ Second Amendment rights, and the pro-abortion lobby,” he said. “His latest false statement about Republicans should come as no surprise to anyone who is paying attention, and we’re happy he has finally shred all pretense of being a conservative.”

While the motives of the shooter in Dayton’s entertainment district remain unclear, the suspect in the El Paso shooting is thought to have posted an anti-immigrant screed on 8chan, an online messaging board known for its racist, bigoted and anti-Semitic content, authorities said.

In March, Trump was asked whether he thinks white nationalism is a rising threat.

He responded: “I don’t really. I think it’s a small group of people that have a very serious problem.”

Mick Mulvaney, the White House acting chief of staff, defended Trump’s assessment on Sunday and dismissed critics who said the president bore some responsibility for the mass shootings.

“I don’t think it’s at all fair to sit here and say that he doesn’t think that white nationalism is bad for the nation,” Mulvaney said on ABC’s “This Week” program. “These are sick people. You cannot be a white supremacist and be normal in the head.”

In a scripted speech Monday, Trump more forcefully condemned bigotry and white supremacy: “Hatred warps the mind, ravages the heart and devours the soul.”

In his tweets, McCollister said Republicans “all like to cite Abraham Lincoln’s Republican lineage when it is politically expedient but NOW is the time to ACT like Lincoln and take a stand.”

Felicia Sonmez contributed to this report.