The most serious threat for Rand Paul’s prospective presidential campaign doesn’t come from Chris Christie, Jeb Bush, Paul Ryan or Ted Cruz. It actually comes from his own father—former Congressman Ron Paul.

In the midst of the Ukraine crisis and Russia’s annexation of Crimea, the three-time failed presidential candidate has enthusiastically cooperated with Kremlin propaganda—appearing on the Russia Today television network to defend President Putin’s aggressive maneuvers and blaming the United States, not Russia, for turmoil in Ukraine.

Meanwhile, the Ron Paul Institute for Peace regularly justifies every turn in Moscow’s policies and features a board-member who simultaneously directs a pro-Putin, Russian funded lobbying group in Paris. If Rand Paul wants to become a credible candidate for commander in chief he must affirm that he’s part of the American, foreign policy mainstream and break—decisively—with his own father’s crack-pot, pro-Russian isolationism.