Sitting in his Capitol Hill office, Sen. Joe Lieberman (I-Conn.) seems content. Although his time in the Senate is coming to an end, he is fully engaged in the national security issues that have been the core of his agenda (and will be of his legacy). Yesterday, he introduced Sen. Marco Rubio (R-Fla.) at a major foreign policy address that he easily could have delivered. He recently took a trip to Syria and that is where our discussion begins.

He is blunt: “I am very disappointed at where we are on Syria.” Three weeks ago he went to Syria and Turkey to observe for himself and speak with leaders in the Free Syria Army. Lieberman glumly reports that without U.S. action, “almost no one is doing anything” to assist the opposition. When some cash comes in to the opposition, it can buy some light arms, but this is no match for Bashar al-Assad’s troops. “It is a desperately unfair fight,” he notes.

He dismisses the blasé attitude of many in Washington who think Assad will go “sooner or later.” Given the way things are going, Lieberman says that there is a greater chance now that “he could go as a result of natural death” than be pushed out.

Meanwhile, in refu­gee camps in Turkey, Syrians whose families, friends and neighbors are being slaughtered “feel fury” against the passive West, he says. He is convinced that “a lot of countries would think of doing something,” such as arming the opposition and setting up protected zones for civilians, but they “are not going to act without the U.S.” He pulls no punches: “A mass atrocity is going on.” He says that in this case our national strategic interest in bringing down Iran’s closest ally coincides with our humanitarian obligations. “[Sen. John] McCain and I and others will continue to press in every way we can,” he vows. But so far the Obama administration seems immovable.

We turn to Iran. He acknowledges the concern that if talks drag out Iran will conclude we are unserious and will continue full steam ahead with its nuclear weapons program. So how do we prevent the rope-a-dope game? Lieberman begins with the premise that if Iran “is approaching a nuclear weapons capability, then we have to act militarily” unless Iran in essence surrenders its program. “They should never feel we are turning down economic and diplomatic pressure” while talking,” he says.

In this he thinks Congress has a role. Either by passing a resolution explicitly opposing a “containment” strategy or by adding “another layer of sanctions,” he contends, it is vital for Congress to act before the May 23 talks. That, he believes, is the only way to convey American resolve.

We then shift to the presidential election. He is staying out of it, he tells me. That said, last year he did weigh in on the pages of The Post with a piece on religion and politics, and specifically on the constitutional prohibition on a “religious test” for office, defending Mitt Romney against attacks on his Mormonism.

It is a subject that still animates him. The issue — not assessing candidates based on their faith but on their public values and personal views — is “fundamental to what this country is about,” he emphasizes. He explains that at a time when some colonies had established religions and religious tests for officials, the Founders explicitly forbade religious tests and included religious freedom in the First Amendment.

He notes that one after another, religious minorities have been accepted at the highest levels of government. He notes the horrible bigotry that Al Smith faced was put aside with the election of John F. Kennedy Jr. This was followed by Jimmy Carter, an overtly evangelical president. And, of course, it was nearly repeated when he, an Orthodox Jew, ran as vice president.

He recalls during the 2000 campaign when a reporter asked him a theological question about Judaism. Uncharacteristically he answered. Afterward, he thought, “Damn it. I shouldn't have answered it.” For one thing, he jokes, some in the Jewish community were upset he got the answer wrong. But more important, he tells me that he should have stuck to his standard line: “I’m running for vice president, not chief rabbi.” He is adamant that a presidential election is not the time for grilling candidates on theology. “When you start to get into the intricacies of a religion I think you’ve gone over the line.” The exploration of the religious dogma of a candidate’s faith, he says, “is not relevant.” Moreover, he asserts, “it’s inconsistent with American values.”

Lieberman has argued that what is relevant is what the candidate has done and what his values are, which may come from a variety of sources and experiences. In the case of Romney, Lieberman specifically rebukes Montana Gov. Brian Schweitzer’s comments about polygamy: “He went over the line.” Lieberman says, “The rest of us have an interest in not standing idly by” in the face of either direct attacks on a candidate’s religion or in the case of a “whispering campaign.” He says he remains “particularly interested ” in the issue because he was “treated so fairly” in the 2000 race.

He concludes, “Romney is running as an American, not a Mormon. He’s not going to call the elders in Salt Lake” for political advice. If it does become necessary for Romney to speak on the issue (he did in the 2008 primary), Lieberman, with his characteristic smile, says Romney should have confidence “in the fairness of the American people.”