Mr Kelly, a former astronaut, is leading Ms McSally in the polls and appears set to replace the former fighter pilot, who was handed the Senate seat after the resignation of Jon Kyl, who was himself appointed following the death of John McCain in 2018 before stepping down.
After being called on stage by Mr Trump, Ms McSally told the crowd: “And you know that other choice is Joe Biden and my opponent Mark Kelly who would be Chuck Schumer’s 51st vote to ram through their radical agenda, to pack the courts, open the borders, to pass the green bad deal tax increases, take away our Second Amendment, you know that and Arizona is not going to let that happen.”
However, for Mr Kelly to be the 51st Democrat in the Senate presupposes the Republicans losing control of the chamber in November’s election – the GOP currently holds 53 seats.
Mr Trump looked on and made no comment as Ms McSally spoke. Despite polls suggesting he may lose the White House to Mr Biden and that the Senate is hanging in the balance, he has regularly insisted that the Republicans will easily hold both.
Mr Kelly, the husband of former congresswoman Gabby Giffords who resigned after surviving an assassination attempt in 2011, has vastly out-raised Ms McSally in their race.
Her campaign was mocked recently when it ran an advert that mistakenly featured Mr Kelly’s twin brother Scott, who is also a former astronaut.