Speaker Mike Johnson may not have a functional majority in Congress, but his job is similar to the Republicans who preceded him in at least one respect: The duties include the difficult task of managing Donald J. Trump.

Mr. Johnson on Friday will travel to Mar-a-Lago, Mr. Trump’s Florida estate, to join him for what the speaker has billed as a “major announcement on election integrity.” No further details have been forthcoming.

The two men had been planning to get together for a political meeting, but Mr. Johnson’s team suggested a joint public appearance on a topic Mr. Trump cares deeply about, according to two people familiar with the planning.

It will afford Mr. Johnson the opportunity to stand shoulder to shoulder with Mr. Trump at a precarious moment in his speakership, as he works to corral a minuscule and deeply divided majority around a legislative agenda many of them oppose — all while facing the threat of an ouster from Representative Marjorie Taylor Greene, a far-right Georgia Republican and ride-or-die Trump ally. Making matters even trickier, Mr. Trump, the former president and presumptive Republican presidential nominee, is helping to undermine that agenda.

Even so, Republicans generally consider it good and politically helpful to be physically near Mr. Trump.