Senate Majority Leader Mitch McConnell has started selling “Cocaine Mitch” T-shirts for his reelection campaign, embracing one of the more memorable attacks on him and signaling strength as he prepares to run for reelection.

Eyeing a seventh term, the Kentucky Republican has embraced the Trump agenda and thrilled conservatives with his mastery of judicial nominations, paving the way for two of President Trump’s Supreme Court picks and more than 100 lower-court judges.

He’s also taken care of a high-profile home-state issue by winning legalization of industrial hemp, helping leave Mr. McConnell, who’s had some rough re-elections in the past, in much stronger position this time.

“It would be a long shot betting on anyone other than McConnell and that is the reality of the situation,” said Dewey M. Clayton, professor of political science at the University of Louisville.

Mr. McConnell kicked off his 2020 campaign last month with an online video touting his decision to refuse action in 2016 on Merrick Garland, then-President Barack Obama’s pick to replace late Supreme Court Justice Antonin Scalia.

That controversial move cleared the way for Mr. Trump to put Justice Neil M. Gorsuch onto the high court — after Mr. McConnell triggered the “nuclear option” to alter Senate rules and break a Democratic filibuster.

“He has gotten a lot of mileage I think from the Supreme Court and judges and the appointment process throughout the federal judiciary, but certainly the Merrick Garland fight and then subsequent Gorsuch appointment has paid tremendous dividends,” said Scott Lasley, political science professor at Western Kentucky University.

Mr. Lasley said Mr. McConnell still shouldn’t be considered a darling of grassroots conservative activists, but said he has silenced some of his most vocal critics.

“He has earned points with them, and I think he has done enough for Trump to at least strengthen his hand,” the professor said.

Mr. McConnell, usually a stiff campaigner, is also showing signs of loosening up this year with the “Cocaine Mitch” apparel — a reference to the bizarre attack by Don Blankenship, a one-time candidate for the GOP’s Senate nomination in West Virginia.

Mr. Blankenship had tried to connect Mr. McConnell to reports of 90 pounds of cocaine found in Colombia on a ship owned by a company tied to Mr. McConnell’s father-in-law.

The usually staid Mr. McConnell on Wednesday leaned into the jibe, with his campaign announcing the T-shirts that read “MITCH” on the front and “Team Mitch Cartel Member” on the back. It features a cartoonlike portrait of a faceless Mr. McConnell, sporting a black button up shirt, collar undone — surrounded by a cloud of white dust.

“A year ago, a legend was born,” the McConnell campaign wrote on Twitter. “Own your own piece of history. #CocaineMitch.”

The campaign site also had “Cocaine Mitch” themed stickers for decorating computers and windows.

Democrats maintain Mr. McConnell is vulnerable next year, saying the Republican has been on the wrong side of issues such as health care, entitlement programs and tax cuts, and accusing him of putting the interests of big corporations and wealthy special interests ahead of his constituents.

“Mitch McConnell has lost touch with Kentucky, his record has made him one of the most unpopular senators in the country, and voters will hold him accountable in 2020,” said Stewart Boss, spokesman for the Democratic Senatorial Campaign Committee.

The DSCC, though, has yet to find a candidate.

Speculation has swirled around the possibility of sports-radio host Matt Jones or former Marine pilot Amy McGrath entering the race.

A group called the Ditch Mitch Fund launched a campaign earlier this year to draft Mrs. McGrath, and vowed to lead a “massive” online fundraising effort on her behalf.

The group did not respond to request for comment, nor did the McConnell campaign.

Ms. McGrath proved to be a strong fundraiser in her congressional bid last fall, but ended up falling in one of the state’s more Democratic-friendly congressional districts, raising questions about her strength in a statewide race.

“I don’t know what Democratic they are going to find to walk the plank just for the party’s sake,” said Ted Jackson, a Kentucky-based GOP strategist. “Nobody is unbeatable, but if anyone is unbeatable, then it is Mitch McConnell this election.”

The senator’s latest fundraising report shows he has $5.5 million cash on hand, putting him on solid financial footing as he awaits an opponent.