• "I think that the Republicans have a lot to do now to repair this breach," GOP pollster Frank Luntz told CNBC on Thursday.
• "This is a bad time for this country," Luntz said. "It's a bad time for the Republican Party."
• The House and Senate ultimately resumed sessions to confirm Joe Biden's victory early Thursday morning.

Some Republicans in Congress must offer explanations for why they did not more forcefully condemn President Donald Trump's false election claims prior to the riot at the U.S. Capitol, GOP pollster and strategist Frank Luntz told CNBC on Thursday.

"I think that the Republicans have a lot to do now to repair this breach," Luntz said on "Squawk Box." "They have a lot to do to explain why they did not stand up to the president before this, why these protests were allowed to get out of control like this."

The riots on Capitol Hill erupted Wednesday afternoon after supporters of Trump came to Washington to protest Congress' finalization of the November presidential election results. Trump encouraged the gathering, tweeting about it for weeks including one Dec. 19 message when he said the protest "will be wild."

In a speech at the rally Wednesday morning, Trump continued to push his baseless narrative that he would have defeated President-elect Joe Biden if not for widespread voter fraud. He vowed again to never concede the election to Biden. "We will stop the steal," he said upon taking the stage.

Although Trump supporters' breach of the U.S. Capitol caused an hourslong halt to the finalization of the Electoral College vote, the House and Senate ultimately resumed their sessions to confirm Biden's victory early Thursday morning. Some Republicans still objected to Biden's wins in Arizona and Pennsylvania — but some GOP senators, such as Kelly Loeffler who lost her seat in Georgia, reversed their positions in the wake of the riots.

"This is a bad time for this country. It's a bad time for the people's house. It's a bad time for the Republican Party," Luntz said. "This morning, I know that there are a lot of people with a lot of regret on their hands, and hopefully, hopefully, the person who regrets it the most is the president of the United States."

Shortly after Congress finalized Biden's victory, Trump said in a statement there would be an "orderly transition" of power. However, he again falsely stated "the facts" support his claim that he lost to Biden only because of widescale ballot fraud.

Luntz has been warning of issues for the Republican Party even before supporters of Trump stormed the Capitol, causing its evacuation and the suspension of a constitutionally mandated session. On Tuesday, he said "the next 48 hours are going to be among the worst for the GOP," referring to the Georgia Senate runoff elections and to the plans of some Republicans to object to the Electoral College votes.

Both Democrats in Georgia are projected to defeat their GOP opponents, according to NBC News projections, which would give the Democratic Party a majority in the Senate. "This is a lesson for the Republican Party of what's likely to come if they continue to behave this way," Luntz said Wednesday morning in response to the Georgia results.

Luntz doubled down on his outlook Thursday: "We have never seen a situation where Americans — Americans — are attacking their critical institution and I think that's going to have reverberations among swing voters."