Image credit: Manuel Balce Ceneta/AP Photo

It's been a busy 24 hours for Sen. Rand Paul.

First the Kentucky Republican delivered the "tea party response" to President Obama's State of the Union address Tuesday night, webcast by the group Tea Party Express.

Today Paul announced he'll block the confirmation of John Brennan, Obama's nominee to head the Central Intelligence Agency, until Brennan says whether he believes the president has authority to kill Americans on American soil.

"I have asked Mr. Brennan if he believed that the President has the power to authorize lethal force, such as a drone strike, against a U.S. citizen on U.S. soil, and my question remains unanswered. I will not allow a vote on this nomination until Mr. Brennan openly responds to the questions and concerns my colleagues and I share," Paul said in a statement released to reporters by his press office on Wednesday.

"Before confirming Mr. Brennan as the head of the CIA, it must be apparent that he understands and will honor the protections provided to every American by the Constitution," Paul said.

Brennan came before the Senate Intelligence Committee last week at a sensitive time for the U.S. intelligence community, after the revelation that Obama's Office of Legal Counsel had advised that it's O.K. to kill American citizens without any judicial proceedings. The U.S. did indeed kill such a person in 2011, when Anwar al Awlaki, a U.S. citizen and Muslim cleric reported to be an al Qaeda operative, was assassinated by an American drone in Yemen.

Brennan defended America's drone policy at his confirmation hearing last week, when multiple senators pressed him on the policy of assassinating Americans linked to terrorist groups.

"Any American who joins al Qaeda will know full well that they have joined an organization that is at war with the United States," Brennan said last Tuesday. "Any American who did that should know well that they in fact are part of an enemy … and that the U.S. will do anything that is possible to destroy that enemy to save American lives."

While drones and extrajudicial killings were a major topic at the Intelligence Committee hearing, killings on U.S. soil-as Paul has specifically asked about-were not a focus.

Paul seems to have first asked Brennan this question yesterday. In January, Paul sent Brennan a letter asking numerous questions about assassination authority. Yesterday, he sent a follow-up that included a question about killings on U.S. soil, specifically.