During a lengthy op-ed published by IJ Review on Monday, Paul suggests that supporting Trump is a "gamble," noting that the businessman has repeatedly shifted his party affiliation over the years.

"It is refreshing to hear someone speak truth to power, to transcend Washington-speak, and cut through the staidness of our politically correct world but not when it is all blather, non-sequitur, and self-aggrandizing bombast," Paul wrote.

"Donald Trump is showing he isn’t suited to lead the country, and I think we all need to discuss why. Frankly, it sounds too much like he is someone used to bullying to get his way. What do you do to a bully? You stand up to him. That’s what I did on the debate stage, and I was the only one," Paul added.

Paul initially shied away from commenting on Trump's previous controversial remarks several weeks ago, instead dinging the media several times for its coverage of the celebrity real estate tycoon. That strategy apparently shifted heading into Thursday's debate, during which Paul interjected seconds in to accuse Trump of "hedging his bet on the Clintons" by not vowing to support the eventual GOP nominee. In another exchange during the debate, after Paul interrupted the businessman, Trump shot back, "I don't think you heard me. You're having a hard time tonight."

Paul has hit back, opening fire on Trump during a campaign stop over the weekend and labeling him a "fake conservative" during a Sunday show appearance.

"I was there at the first Tea Party in 2007 and I’ll be damned if I’m going to stand passively by and watch the movement destroyed by a fake conservative," Paul wrote in his op-ed Monday.

"The Tea Party erupted over dissatisfaction with false conservatives. It amazes me that anyone in the Tea Party movement could possibly consider Clinton/Reid/Pelosi supporter Donald Trump for President," Paul wrote.

"This is a guy who said in 1999 that he was a strong supporter of the United Nations. He was for partial birth abortion before he was against it. He lavished praise on the bank bailouts. He was for Obamacare before he was against it and has said he’s 'liberal on health care,' " he added.