The five living former United States presidents joined forces on Thursday to start a hurricane recovery effort to raise money for victims of Hurricane Harvey in Texas.

The campaign, One America Appeal, began with a public service announcement featuring the presidents during the first N.F.L. game of the season on Thursday night. “People are hurting down here,” former President George W. Bush, who lives in Dallas, said in the video, “but as one Texan put it, ‘We’ve got more love in Texas than water.’”

The appeal was a rare showing of unity in American politics, and President Trump, who has disregarded traditional presidential decorum and has criticized some of his predecessors, endorsed their effort. “We will confront ANY challenge, no matter how strong the winds or high the water,” Mr. Trump said on Twitter on Thursday night. “I’m proud to stand with Presidents for #OneAmericaAppeal.”