The presumptive nominee to become America’s next defense chief got a preview of some of the opposition he may run up against in confirmation hearings as Republicans took to Sunday morning talk shows.

The Senate’s Republican leader Mitch McConnell said he was reserving judgment on whether to support former Sen. Chuck Hagel, the front-runner to be the next defense secretary, and predicted that his former colleague would face serious questions about his stands on Iran and Israel.

Another Republican senator said he didn’t rule out the possibility of a GOP filibuster to bar a vote on Hagel’s nomination.

President Barack Obama may round out his new national security leadership team this coming week, with a nomination for Pentagon chief expected and a pick to lead the Central Intelligence Agency possible. Democratic officials told the political news website Politico Sunday that Obama settled on Hagel to succeed Defense Secretary Leon Panetta, with an announcement expected Monday.

McConnell said any defense nominee must have “a full understanding of our close relationship with our Israeli allies, the Iranian threat, and the importance of having a robust military.”

McConnell told ABC television’s “This Week” that Hagel, a Nebraska Republican who left the Senate in 2009, has “certainly been outspoken in foreign policy and defense over the years. The question we will be answering, if he’s the nominee, is do his views make sense for that particular job?”

McConnell said he would “wait and see how the hearings go and see whether Chuck’s views square with the job he would be nominated to do.” He added: “I’m going to take a look at all the things that Chuck has said over the years and review that, and in terms of his qualifications to lead our nation’s military.”

Sen. Lindsey Graham (R-SC) said he didn’t rule out the possibility of a Republican filibuster of Hagel’s nomination.

“But when you put all the statements together, you have somebody who is very antagonistic towards the state of Israel and the issues we jointly face,” Graham told CNN.

Obama, in an interview that aired last Sunday on NBC’s “Meet the Press,” called Hagel “a patriot” who “has done extraordinary work” in the Senate and on an intelligence advisory board.

Illinois Sen. Dick Durbin, the second-ranking Senate Democrat, told CNN’s “State of the Union” that Hagel “is a serious candidate if the president chooses to name him.”

Hagel has criticized discussion of a military strike by either the US or Israel against Iran. He also has backed efforts to bring Iran to the table for talks on future peace in Afghanistan.

Some lawmakers have been troubled by his comments and actions on Israel, including his reference to the “Jewish lobby” in the United States.

Sen. Ted Cruz (R-TX) said on “Fox News Sunday” that he found it “very difficult to imagine a circumstance in which I could support (Hagel’s) confirmation.”

“It’s interesting, the president seems bound and determined to proceed down this path despite the fact that Hagel’s record is very, very troubling on the nation of Israel,” Cruz said. “He has not been a friend to Israel. And in my view the United States should stand unshakably with Israel.”

Obama has nominated Sen. John Kerry as his next secretary of state, in what was the president’s first step in filling out his second term Cabinet and national security team.

Kerry, as well as the nominees for the Pentagon and CIA, must be confirmed by the Senate.

A Senate Democratic official told Politico, however, that Hagel’s statements have rallied opposition by pro-Israel groups and gay-rights groups.

“I don’t think Dems just fall in line. Ultimately, he may be confirmed. But at this stage, his fate is totally up in the air. He will really have to work hard to overcome some of his previous statements and positions,” the Senate Democrat was quoted saying.