Sen. John McCain threatened Thursday to block a second term for Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, after a testy exchange over the Obama administration's response to the war in Syria.

McCain (R-Ariz.), a member of the Senate Armed Services Committee and a former presidential candidate, told reporters that he would place a hold on Dempsey’s nomination for a second two-year term unless the Army general divulges his private opinions on the best course for the White House to take in Syria.

During a confirmation hearing earlier Thursday, Dempsey sidestepped questions from McCain and other Republican senators about what course of action he has recommended that President Obama take in Syria. Dempsey said the administration was still weighing its options and that “it would be inappropriate for me to try to influence the decision with me rendering an opinion in public about what kind of force we should use.”

Dempsey’s response frustrated McCain, who said the general had pledged to share his personal views with the Armed Services Committee, even if they were at odds with the administration’s public stance.

“I want him to answer the question,” McCain told reporters after the hearing. He said he would block a vote on the renomination “until Gen. Dempsey responds to the legitimate questions that he committed to do.”

McCain and other senators, including committee Chairman Carl Levin (D-Mich.), have pressed Obama to intervene militarily in Syria by imposing a no-fly zone and giving more effective aid to rebels seeking to topple President Bashar al-Assad. More than 100,000 people have died in the civil war.

Pentagon leaders have said it would be just a matter of time until Assad is forced out. But Thursday, Dempsey acknowledged that Assad has since gained the upper hand and said it was “likely” that he would be in power a year from now.

“Currently, the tide seems to have shifted in his favor,” Dempsey said.