TAMPA — The Romney campaign has been reluctant, to put it mildly, to spend time on national security during the presidential campaign. But at the Republican National Convention it has begun to make its top national security advisers available to describe Mitt Romney’s stance on foreign policy.

Former Missouri senator Jim Talent (R-Mo.) held a session today on defense issues, dubbing President Obama’s willingness to proceed with defense sequestration an act of “breathtaking irresponsibility.” And the most influential foreign-policy adviser within the Romney inner circle, the former special envoy to Sudan, Richard Williamson (accompanied by Richard Grenell, who was briefly with the Romney team) sat down for lunch with several of us from The Post. He offered the most complete outline of a Romney foreign-policy vision since the candidate’s speech nearly a year ago at the Citadel.

Williamson didn’t miss the chance to remind us that he worked as a youth on Ronald Reagan’s 1976 platform and has held an impressive list of foreign-policy posts. The message was implicit: This is a grown-up who, unlike the Obama team, knows how the world works. He ruefully remarked, “Valerie Jarrett and David Axelrod are the [president’s] most important foreign policy advisers,” the first of many jabs at the president for insufficient seriousness toward national security.

Williamson candidly acknowledged that the Romney campaign is not spending a great deal of time publicly on national security, although he hastened to reel off a list of discrete foreign-policy speeches and statements. He said that for the Obama camp a good day is “any day they are not talking about the economy.” It is an understandable political consideration not to, as Williamson put it, “crowd out” the most important issue to voters and the issue on which Obama is most vulnerable — namely, the economy. But that reticence has left many wondering what Romney believes and how much political capital he’d devote to foreign-policy issues.

Williamson ticked through a number of fundamental differences between the president and Romney.

He began bluntly, “Romney believes in American exceptionalism.” He cited the oft-repeated Obama line that he believes “in American exceptionalism, just as I suspect that the Brits believe in British exceptionalism and the Greeks believe in Greek exceptionalism.”

He conceded that, as the election has drawn closer, Obama has occasionally altered his rhetoric, but Williamson insisted that what is in “the heart and soul of Barack Obama” is the conviction that we are merely one of many nations. He cracked, “How’s that working out for 19,000 Syrians?” He emphasized that Romney is convinced that “America is better off, our friends better off and the world is better off” when America asserts its influence.

By being risk-averse in Syria and elsewhere, Williamson argued, “You get more risk.” Our options are fewer now, he contends, with regard to Syria and Iran. He was quick to add that he was not arguing for “boots on the ground” but for a more active and robust pursuit of American interests.

Next in the list of dramatic differences between the candidates, he said, is that “the governor believes in peace through strength,” adding the familiar adage that we “never got into a war because we were too strong.” He said every president has subscribed to this principle since the end of World War II, except two. “Jimmy Carter and Barack Obama are the outliers,” he said.

Williamson congratulated “everyone who spent 10 years” seeking Osama bin Laden, as well as the president. But that, along with the president’s increased use of drones, do not a foreign policy make, he argued.

Williamson also stressed that Romney will not be lulled into misperceiving the motives of other powers: “He knows that, just like people look out for their own interests, so do countries.”

He made the case that, in ignoring the Green Movement in Iran, straining to engage the Iranians and ignoring Iranian threats to annihilate Israel, Obama badly misread the Iranian regime and has emboldened its leaders. He recollected Obama’s hot-mike moment with Russian President Dmitry Medvedev (“On all these issues, but particularly missile defense, this can be solved, but it’s important for him to give me space. This is my last election. After my election, I have more flexibility.”). Williamson said tersely, “The Iranians thought he was talking to them.”

In the back-and-forth with Post journalists, Williamson alternated between his foreign-policy analyst persona and his job as chief foreign-policy guru for the campaign. In his analyst role, he explained that Obama has relied on engagement, multilateralism and international law. “That is not a foreign policy,” he stressed. “These are tools of a foreign-policy strategy.” Williamson made the case that Obama has failed to prevent Iran’s acquisition of nuclear weapons and ignored or actively hindered (by cutting off aid for civil-society development) progression to a more democratic Egypt. Ironically, when Williamson spoke about utilizing influence, he was careful to stress the “soft power” tools that Obama has talked about but never put to use.

We asked about Romney’s core conviction and willingness to use political capital for national-security aims. He was forceful, perhaps more so on any other issue, when it came to the rebuilding of American defenses. “He doesn’t think 20 percent of the budget should have 50 percent of the cuts.” Williamson said emphatically, “His statements on sequestration are deeply felt.”

He declared confidently that Romney would, in fact, use his influence to avoid damaging cuts to defense and to rebuild an aging military force. He also noted the earlier comments of Talent at the convention, making the case that ample money could be saved from reforms, particularly in procurement, to use in shoring up our crumbling Air Force and Navy.

On China, Romney has used some boisterous language to describe his refusal to accept unfair trade practices. Does he really mean it, or is this posturing for an election? “China is shocked,” Williamson said, when we don’t object to its practices, and we should forcefully object to currency manipulation and favoritism toward state-owned industries. Romney knows how to negotiate without getting into a trade war and will not be timid about expressing our interests, he said, adding, “Why can’t we have an adult relationship with Beijing?”

In a sense, Williamson’s pitch about Romney can be boiled down to: Why can’t we have an adult foreign policy, one that advances U.S. interests, doesn’t practice wishful thinking about our adversaries, doesn’t shirk from defending our values and is willing to defend defense? His answer is, of course, that we can. With a different president.