Before Tuesday night's CNN Democratic debate, the Ohio congressman was the only candidate with his hands at his sides as the Star-Spangled Banner was performed.
Critics were quick to jump on Ryan, including "The View" panelist Meghan McCain.
Her statement was echoed by Ari Fleischer, the former White House press secretary under George W. Bush, who tweeted: "Rep. Tim Ryan didn’t put his hand over his heart during the national anthem. I guess he’s appealing to the Kaepernick wing of the Democratic Party."
Ryan also got into a couple of heated exchanges with Vermont Sen. Bernie Sanders over health care, with the latter at one point shouting, "You're wrong!"