A year ago, both Sen. Rand Paul and Sen. Ted Cruz were standing together against the Obama administration during Paul's epic drone filibuster.

Now, the two senators are fiercely debating over Ronald Reagan's foreign policy legacy.

For months, people close to the Paul and Cruz teams have whispered in Washington about a growing feud between the two conservative senators.

That feud officially boiled over after Paul, R-Ky., fired back at comments that Cruz, R-Texas, made criticizing Paul's foreign policy views on Sunday.

"I'm a big fan of Rand Paul. He and I are good friends. I don't agree with him on foreign policy," Cruz said in an interview aired Sunday on ABC's "This Week."

During a foreign policy speech last Thursday, Cruz pointed out that he was staunchly with Ronald Reagan on foreign policy -- explicitly explaining that he did not identify his foreign policy views with either Sen. John McCain or Paul.

Paul fired back in a Breitbart News op-ed on Monday, and although he was careful not to mention Cruz by name, it was obvious who he was referring to.

"I don’t claim to be the next Ronald Reagan nor do I attempt to disparage fellow Republicans as not being sufficiently Reaganesque," he said. "But I will remind anyone who thinks we will win elections by trashing previous Republican nominees or holding oneself out as some paragon in the mold of Reagan, that splintering the party is not the route to victory."

Paul was referring to Cruz's recent comments regarding former Republican presidential candidates Mitt Romney, John McCain, and Bob Dole.

Paul further criticized those who were questioning President Obama's response to Russian President Vladimir Putin's aggression in Ukraine.

"[S]ome politicians have used this time to beat their chest," he wrote. "What we don't need right now is politicians who have never seen war talking tough for the sake of their political careers."