It's no secret that Donald Trump hasn't always gotten along with members of his own Repubican Party. For Sen. John McCain, he doesn't look to be holding back anytime soon with his thoughts about the president.

McCain on Trump

When Donald Trump announced that he would be running in the Republican primary election in June 2015, many high-ranking officials in the party were not pleased. Trump's controversial style and rhetoric caused red flags to be raised, with the GOP reputation on the line. During the early stages of the 2016 presidential election, the former host of "The Apprentice" came under fire for his remarks about John McCain.

"He's not a war hero," Trump said of McCain, who served in the United States Military during the Vietnam War. Trump then appeared to mock McCain for being captured as a POW, stating, "I like people who weren't captured." Since then, the bad blood between the Arizona senator and the president has only continued, which was evident during a recent speech given by McCain who spoke out against "half-baked, spurious nationalism." On Tuesday morning, Trump took part in a radio interviewed and sent a warning to the senator, which was detailed in The Hill on October 17.

While being interviewed on The Chris Plante Show on Tuesday morning, Donald Trump was asked about the latest criticism from Sen.

John McCain, as the president sent back a warning and threat of his own. "I'm being very, very nice," Trump said, before adding, "But at some point I fight back, and it won't be pretty."

Not long after Donald Trump gave his remarks, John McCain wasted no time with a short, but sweet, response. "I've faced far greater challenges than this," he said.

McCain was recently diagnosed with brain cancer, and it appears that the commander in chief is holding back his remarks due to potential backlash. Just last month, McCain came out against Trump's bill to repeal and replace Obamacare, which proved to be the final nail in the president's latest attempt to kill the Affordable Care Act.

As expected, McCain's decision didn't go over well with the president.

Moving forward

While Donald Trump continues to fight with members of his own party, questions remain unanswered in regards to various issues. Health care and tax reform face an uncertain future, with instability growing between the United States and North Korea. As the pressure mounts on the White House, Trump has been unable to increase his approval rating from where it stands at below 40 percent.