Senate Minority Leader Mitch McConnell on Wednesday celebrated Republicans winning control of the Senate and the White House, saying he views the results from the day before as a referendum on the Biden administration.

While Mr. McConnell, Kentucky Republican, has a tenuous relationship with President-elect Donald Trump, he complimented him and his campaign for running a “spectacular race,” saying it was a “sharper operation” than their 2020 effort.

And as he prepares to step down as GOP leader at the end of the Congress, Mr. McConnell said he’s glad he’ll be handing his successor the majority, as leading is “a lot better” from that perch than the minority. 

“It was a hell of a good day,” he said. 

Senate Republicans will have at least a 52-48 majority next Congress after flipping seats in Montana, Ohio and West Virginia. 

And that margin could grow as some Senate races have yet to be called in five states, with Republican candidates leading in Pennsylvania and Nevada.

Democrats are leading in uncalled Senate races in Michigan, Wisconsin and Arizona. 

“The remaining ballots being counted will continue to strengthen Democrats’ standing in our Senate races,” Democratic Senatorial Campaign Committee communications director David Bergstein said in a statement. “When this process of counting the votes concludes, Democrats will have won races in multiple states carried by Trump and successfully limited the GOP’s potential gains on their historically favorable map.”

However the remaining races shake out, Mr. McConnell said he’s “never seen a better performance” from the National Republican Senatorial Committee. He praised Montana Sen. Steve Daines, the committee chairman, for candidate recruitment and his efforts to get them elected. 

“Candidate quality is essential,” Mr. McConnell said. “And I think we had the best candidates everywhere yesterday.”

He also credited the Senate Leadership Fund, the GOP leaders’ aligned super PAC, and related outside groups for raising $425 million and investing it “in all the right places.”

Keeping Democrats from expanding their majority ensures the legislative filibuster is secure and that they won’t be able to make other power grab plays that members of their party wanted, Mr. McConnell said.

“I think one of the most gratifying results of the Senate becoming Republican: The filibuster will stand; there won’t be any new states admitted that give a partisan advantage to the other side; and we’ll quit beating up the Supreme Court every time we don’t like a decision they make,” he said. 

Republicans’ plans to keep the legislative filibuster will make passing their agenda more difficult since they will need 60 votes to overcome any minority opposition. But Mr. McConnell noted that they can still avail themselves of the filibuster-proof budget reconciliation process to pass economic legislation with a simple majority if Republicans retain the House. 

Mr. McConnell seems willing to put his past with Mr. Trump aside to help deliver a GOP agenda. 

“I’m going to do everything I can to help the new administration be successful,” he said.

Yet the outgoing GOP leader signaled some remaining discomfort with Mr. Trump as he dodged questions about his past criticism of him.

Asked if he’s confident Mr. Trump is the best person to deter America’s foreign adversaries, given his opposition to providing aid to Ukraine in its war against Russia, Mr. McConnell demurred. 

“Look, I’m here this morning to talk about the election, and I think I’m going to largely confine it to that,” he said. 

And when asked about his shots at Mr. Trump in his recently published biography, Mr. McConnell said, “I’m not here to do a book review.”

Mr. Trump slammed Mr. McConnell as recently as Sunday when he said at a rally in North Carolina that he would be happy to see the longest-serving GOP leader go since he aided Democrats in enacting too much spending. 

“Hopefully, we get rid of Mitch McConnell pretty soon because he helped them,” Mr. Trump said. “That guy. Can you believe he endorsed me? Boy, that must have been a painful day in his life.”

“What a disgrace,” he said.

Mr. McConnell was not asked about Mr. Trump’s remarks but did get a question on how Republicans taking control of the Senate would change the annual appropriations process. 

“I would hope that we would put a greater priority than the current Senate has on doing the basic work of government, which is deciding how much to spend and getting it done as close to regular order as possible,” he said. 

Mr. McConnell didn’t mention cutting spending. While he would likely support domestic spending cuts, he has signed off on increases to the defense budget. 

Defense and foreign policy are what Mr. McConnell said he plans to concentrate on after he steps down as GOP leader and becomes a rank-and-file senator for the remainder of his term. It’s not clear whether Mr. McConnell will run for reelection in 2026.

“I think this is the most dangerous time since right before World War II,” he said. “Our adversaries — the North Koreans, the Chinese, Russians, Iran and Iran’s proxies — are all talking to each other. They have one thing in common: They hate us, and they want to diminish our role in the world.”

He added, “We need to ramp up defense spending in order to prevent direct conflict with our adversaries. It’s a lot cheaper to prevent war than it is to have one. And so that’s the focus I’m going to have for the next couple of years.”