Donald Trump has vowed to run as a Republican in 2016, but Marco Rubio thinks one of his proposals is better suited to the Democrats.

Appearing on Boston Herald Radio Tuesday, Rubio ripped into Trump's yet-to-be-released tax plan, which is expected to call for a tax hike on the wealthiest earners. The Florida senator said that Trump "should run as a Democrat" with that kind of plan, arguing further that lowering taxes is the real solution.

"I think if someone wants to raise taxes, they should run for the Democratic nomination," Rubio told host Adriana Cohen. "That party loves to raise taxes. I want to keep taxes low."

"I think we need to have the lowest tax burden nation of the industrialized countries," Rubio said. "That means we need to lower our corporate tax rate, lower our personal tax rate, simplify the tax code ... have a pro-family tax code that increases the child tax credit."

"I don't know what problem that solves," Rubio said of the plan. "That seems to me like a solution in search of problem. It doesn't really solve anything. If someone wants to raise taxes, they should run as a Democrat."

Rubio's comments come a week after Trump ruled out a potential third party run for the White House by signing a pledge saying that he will run for the GOP nomination and only the GOP nomination. The 2016 hopeful also said that he is open to being Trump's vice presidential nominee if he were to lose the nomination himself.