Extending a weekslong right-wing meltdown over Taylor Swift’s political preferences, former President Donald J. Trump declared on Sunday that it would be “disloyal” for Ms. Swift to endorse President Biden for re-election, given that Mr. Trump signed legislation that made it easier for artists to collect royalties when their songs are streamed.

“I signed and was responsible for the Music Modernization Act for Taylor Swift and all other Musical Artists,” Mr. Trump wrote on his social media platform, referring to a 2018 bill that passed Congress with near unanimous support from members of both parties. “Joe Biden didn’t do anything for Taylor, and never will. There’s no way she could endorse Crooked Joe Biden, the worst and most corrupt President in the History of our Country, and be disloyal to the man who made her so much money.”

“Besides that, I like her boyfriend, Travis, even though he may be a Liberal, and probably can’t stand me!” Mr. Trump added.

Ms. Swift and the aforementioned boyfriend — Travis Kelce, a tight end for the Kansas City Chiefs, who are playing in the Super Bowl on Sunday — have been the subject of right-wing conspiracy theories for months, since Ms. Swift urged her fans to register to vote and tens of thousands obliged, and since Mr. Kelce appeared in a Pfizer ad campaign urging people to get Covid and flu vaccines.

The theories mushroomed last month as commentators speculated not only that Ms. Swift would endorse Mr. Biden (entirely plausible given that she did so in 2020, though by no means certain) but that shadowy liberal forces were manufacturing her and Mr. Kelce’s fame and romance in order to prop up Democrats and vaccines.

Ms. Swift was a household name long before Mr. Biden became president, and before Mr. Trump ran in 2016.