In a video posted by Downing’s campaign, Flynn cited a family emergency for the cancellation of his scheduled Sunday appearance in Billings.
Trump fired Flynn in February 2017. White House officials said he misled them about his Russian contacts. The former general is one of 19 people charged in the investigation by special counsel Robert Mueller’s investigation into Russian meddling in the 2016 U.S. election.
Flynn pleaded guilty to lying to the FBI.
Downing is one of four candidates seeking the Republican nomination to challenge Democratic U.S. Sen. Jon Tester.
In Saturday’s video, Flynn said Downing’s experience as a combat veteran made him the best candidate.