In an interview earlier this month, Clark, who also served as NATO commander prior to his retirement, called for a revival of internment camps to help combat Islamist extremism in the United States.
"If these people are radicalized and they don't support the United States and they are disloyal to the United States as a matter of principle, fine," he said. It's their right and it's our right and obligation to segregate them from the normal community for the duration of the conflict."
In 2004, Clark campaigned for the Democratic presidential nomination, which ultimately went to then-Senator John Kerry – something Paul said is a positive.
"Gen. Clark ran for president in 2004 and it's probably a good thing he didn't win considering what seems to be his disregard for the Constitution," the former Congressman from Texas wrote in a column published to his website on Monday.
Paul also called out Donald Trump, saying the Republican presidential candidate and real estate mogul "one-upped Clark" when he said that NSA whistleblower Edward Snowden is a traitor and should be treated like one. According to Paul, Trump was implying that the US government should execute Snowden.
Paul launched unsuccessful bids for the Oval Office in 1988, 2008 and 2012.
"Let's hope these threats from Clark and Trump are not a trial balloon leading to a clampdown on our liberties," Paul wrote in Monday's column.
He also cited two "reasons we should be concerned":
One is a bill that would allow the Secretary of State to unilaterally cancel the passport of any American who has "aided" or "abetted" a terrorist organization; the other is a Senate bill that would allow the Secretary of State to cancel the passport of any American who owes too much money to the IRS.
"Canceling a passport means removing the right to travel, which is a kind of virtual internment camp. The person would find his movements restricted, either being prevented from leaving or entering the United States," he wrote.
"Neither of these measures involves any due process or possibility of appeal, and the government's evidence supporting the action can be kept secret."