After the Republican presidential debate in Las Vegas, MSNBC “Hardball” host Chris Matthews did something few, if any, television interviewer has done. He not only pushed Donald Trump hard on the GOP front runner’s past peddling of the racist birther lie against President Obama,  Matthews said how wrong and ugly his escapade was.

“Is Donald Trump honest when he says Barack Obama isn’t a legitimate president?” Matthews asked. “I don’t talk about that anymore,” Trump responded, adding, “Because, you know what? If I do answer it, that’s all people want to talk about…once I answer the question, they don’t want to talk about the economy, they don’t want to talk about all the other things.”

“We Catholics believe in confession,” Matthews continued. “You say you were wrong and you move on. You really believe this guy is an illegitimate president?” Trump continued to not answer the question. As the interview ended, Matthews got in the last word.

Mr. Trump, I do think that’s a blemish on you. I think it’s your original sin because I’m an American and I think our president should be respected. And I think there’s a little ethnic aspect to it and I don’t like it. He’s African American and we’re saying he’s not a real president. I don’t like that. It’s not a good thing about you.

Four years ago, when Trump was entertaining a White House run, he danced with far-right conspiracy theorists who firmly believed Obama was not born in the United States, but in his father’s native country of Kenya thus making him an illegal occupant of the Oval Office. No amount of evidence disabused them of these falsehoods. Not his birth certificate showing he really was born in Hawaii. Not the fact that were he born in Kenya, he would still be an American citizen thanks to his Kansas-born mother. Not even the thorough debunking of every attendant myth attached to the birther lie.

Then, as now, Trump was coarsening national political discourse by erroneously questioning the legitimacy of the president. That’s not to say that birtherism is totally out of Trump’s orbit. While introducing the candidate yesterday at a campaign rally in Mesa, Ariz., Sheriff Joe Arpaio of Maricopa County, Ariz., said his birther investigation is “still going on.” Mind you, that pronouncement came nearly five years after the president released his long-form birth certificate in response to incessant hectoring from Trump.    

Yet, what the bloviating billionaire Big Apple builder did back in 2011 seems quaint compared to the ugliness he has unleashed in the 2016 campaign. There’s no need for me to run down Trump’s every cheap, xenophobic, misogynistic and racist utterance, retweet or mimic.

Still, the Republican front runner’s ability to stoke fear and ride it to the top of the polls is as troubling as the fact that his ugly rhetoric has become the new normal among the GOP. The Post editorial board Thursday put it best when it decried the extremism that now passes for mainstream Republican thought, robbed of its shock value by the unfiltered ravings of Donald Trump,…” Such extremism cannot go unchallenged. Perhaps this is too much to ask or expect during a debate with as many candidates on stage as the Radio City Christmas Spectacular. But when Trump submits himself to an interview, either by phone (ubiquitous) or in-person (rare), he should be held accountable for his past statements and policy pronouncements. Bravo to Matthews for doing so.

Words matter when you run for president. And fear and bigotry are weak foundations upon which to rest a presidency. Trump’s “unfiltered ravings” are a short-term political marvel for him. What’s incalculable is their long-term damage to the Republican Party and to the nation.

Follow Jonathan on Twitter: @Capehartj