Those who died were all on e-bikes. Seventeen cyclists have been killed so far this year, and advocate groups said the deaths should be a rallying cry for safety improvements.

A plan to lower tariffs on imported beef and trade tensions with Canada have compounded some G.O.P. worries about a central issue in the midterms.

It was the final, major event planned for the nation’s 250th anniversary celebrations. The president took a lap.