Former House Speaker Newt Gingrich formally endorsed Sen. John McCain in a video released by the campaign, calling the longtime Arizona senator a "national treasure" and "somebody who's making a real difference" as chairman of the Armed Services Committee.

Notably, Gingrich's endorsement comes two days after Republican presidential nominee Donald Trump declined to endorse the senator. Trump specifically cited McCain's lack of work in support of veterans in refusing to back him. However, Gingrich pushed back against that idea, saying in the 45-second-long video that he knows "how hard" McCain works in support of veterans and the United States military.

"I strongly endorse Sen. John McCain," Gingrich said. "A genuine American hero, a man who has endured a great deal for his country, and a man I work with and watch provide leadership as chairman of the Armed Services Committee."

"I know how hard John works for veterans, for the military, for our national security, and I know that John McCain is a national treasure. Somebody who's making a real difference. A man of great courage who is a patriot, [and] serves his country without fear," Gingrich said. "I hope you'll do everything you can to make sure that Sen. John MCCain continues to work in Washington on your behalf and on the behalf of all Americans."

In recent days, the former speaker and 2012 presidential candidate has been outspoken about the recent missteps by Trump, arguing that he would be better served focusing on Hillary Clinton instead of McCain, Paul Ryan and the family of slain Army Capt. Humayun Khan after his father, Khizr Khan, spoke out against Trump at the Democratic National Convention last Thursday.