It's no secret that President Donald Trump and Senator John McCain have had a bit of a tense relationship over the years. While on the campaign trail, then-candidate Trump said, “He’s not a War Hero. He was a war hero because he was captured. I like people who weren’t captured.” This was in reference to McCain's Navy pilot career when he was held captive for five-and-half years in a North Vietnamese prison, two of which were spent in solitary confinement. The disparagement has continued, even as recently as a few months ago when Trump mocked "dying" McCain.

So, it was easy for people to think that the Arizona senator was taking a jab at Trump when McCain recently told CSPAN-3, "One aspect of the [Vietnam] conflict, by the way, that I will never ever countenance is that we drafted the lowest income level of America, and the highest income level found a doctor that would say that they had a bone spur."

President Trump famously received five draft deferment during the Vietnam war, one of which was due to heel spurs, a variation of the malady that McCain referenced. Trump has previously said it was a bone spur, but declined to further discuss it.

McCain later sought to clarify his statement, explaining, "By the way ... on this issue of people who got deferments from serving in Vietnam.

I was against that 40 years ago, so for you people to say that I'm taking a shot at Trump over that, then you don't know my record."

Trump's and McCain's history

Donald Trump has attacked John McCain several times since he began his presidency. Some recent attacks are related to the former presidential candidate's "no" vote on the Obamacare repeal, just days after it was revealed McCain is fighting cancer.

Beyond that, Trump has historically been a steadfast critic of McCain, tweeting things such as "The very foul mouthed Sen. John McCain begged for my support during his primary (I gave, he won), then dropped me over locker room remarks!"

Their relationship moving forward

If the past is any indication of the future, it's not hard to believe that there will be more friction between war hero Senator John McCain and President Donald Trump in the future.

This is especially true since some large legislative initiatives still need to be passed, including tax reform, healthcare reform, and immigration reform. As we saw with McCain's 11th hour dramatic "no" vote on Obamacare, the President needs as many supporters in his party as he can get, including McCain.

Additionally, McCain is never one to shy away from his convictions, and at times has been outspoken about his criticism of the President. This would lead one to believe that if he indeed did mean to criticize Trump's lack of military service, he would have said so outright. The senator was asked on The View, where his daughter Meghan McCain is a new host, if he was scared of Trump's notorious public retaliations. His reply was a simply laugh.