Republican Sen. John McCain, pictured Tuesday in the U.S. Senate, said Wednesday that Congressman Bernie Sanders had a better track record taking care of veterans than Democratic rival Hillary Clinton. Getty Images

Democratic Sen. Bernie Sanders of Vermont is a stronger presidential candidate for Democratic voters when it comes to advocating for veterans, Sen. John McCain said Wednesday. McCain, an Arizona Republican who served in the Vietnam War and was held as a prisoner of war for over five years, has long been an outspoken defender of veterans' rights.

McCain pointed out that Sanders, who serves on the Committee on Veteran Affairs, had helped pass bills protecting veterans with bilateral support. “To my knowledge, I know of no activity, legislative or otherwise, that Hillary Clinton was engaged in during her time as a United States senator,” McCain said, as reported by the Hill.

As a senior senator and 2008 Republican presidential nominee, McCain has taken on a leading role in discussions in the run-up to the 2016 presidential election. The Republican leader defended soldiers when GOP candidate Donald Trump in July said, "I like people who weren’t captured,” in reference to McCain's status as a war hero. McCain responded by saying only that the real heroes were those who sacrificed their lives in protection of their country.

McCain criticized Clinton's handling of the veteran affairs hospital scandal that occurred in 2014, in which a bungling hospital administration kept veterans waiting for many months to see doctors.

Clinton said last week the problems in VA hospitals were not particularly widespread, leading McCain to retort, “I would say that if Hillary Clinton really believes the comments that she made, I don’t see how any veteran who cares about their fellow veterans could possibly have any good things, nor could support her quest for being commander in chief."

Sanders, a self-proclaimed democratic socialist originally from Brooklyn, has garnered support in his campaign so far, particularly from young voters who see Clinton as an establishment candidate. Sanders' laid-back attitude and frank approach to politics has charmed voters who said they feel disillusioned with the current leadership.

Clinton has been gaining ground in the past week, however, surging to a 41-point lead in Iowa in a Monmouth University poll published Tuesday.