A U.S. military plane lands on the flight deck of the USS Carl Vinson aircraft carrier in the Persian Gulf, Thursday, March 19, 2015. (Hasan Jamali/AP)

Robert Kagan is a senior fellow at the Brookings Institution and a contributing columnist for The Post.

A guy challenges Groucho Marx: “Are you a man or a mouse?” Groucho responds: “You put a piece of cheese down there and you’ll find out.”

In the next couple of weeks, we’ll all find out about the Republican Party. For the past few months, Republicans in Congress and those preparing to run for president have been staking out what some would call a “hawkish” position on foreign policy. After flirting for a couple of years with the anti-interventionism of Sen. Rand Paul (R-Ky.), most of the party’s leading politicians have been lambasting President Obama for doing too little to fight the Islamic State and defend Ukraine while trying to strike a bad nuclear deal with Iran. On these issues, they have mostly been in sync with the public, which may be slowly and tentatively shedding its hostility to greater involvement abroad, at least when it comes to fighting terrorism.

So far, however, this hawkishness has been mostly rhetorical. With few exceptions, Republicans have not been very clear about what they would do differently than the Obama administration. And they have not talked much about the possible costs of an alternative approach. So one is left to wonder whether the new tone is based on genuine conviction about the nature of the threats facing the world and America’s essential role in meeting them, or whether many Republican politicians just figure that hawkishness is a great way to run against the Democratic nominee in 2016.

As it happens, we now have an opportunity to find out. Congress is debating the federal budget, and part of that debate concerns defense spending. Until recently, the Republican leadership in both houses favored maintaining “sequester” spending levels, which would force further sharp cuts to an already ravaged defense budget. A House Budget Committee proposal this week sought to use increases in emergency contingency funding to smooth this over, but the hard spending caps would remain in place this year and in future years. At those budget levels, as successive secretaries of defense and service chiefs have warned, the United States’ ability to defend its interests would be gravely in doubt.

Meanwhile Obama, whom Republicans like to castigate as weak, is actually proposing an increase in the defense budget, to $561 billion — or $38 billion above the sequester caps. In a statement to the Senate Armed Service Committee this month, Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, said the president’s request is “what we need to remain . . . at the bottom edge of manageable risk to our national defense. . . . [T]here is no slack. There is no margin left for error, nor for a response to strategic surprise.” In other words, the president’s request is itself inadequate, but it’s still higher than what Republicans propose. Apparently, Republican congressional leaders are willing to have the U.S. armed forces operate below what our top man in uniform calls “the bottom edge of manageable risk to our national defense.”

Last year, the National Defense Panel, a bipartisan congressionally appointed commission co-chaired by former defense secretary William J. Perry and former U.S. Central Command leader Gen. John P. Abizaid, unanimously recommended that Congress repeal the sequester and return, “at a minimum,” to the budget prepared by former defense secretary Robert Gates in fiscal 2012, which would have brought fiscal 2016 spending to $640 billion. In recent weeks, Sen. John McCain (R-Ariz.) and Rep. Mac Thornberry (R-Tex.), the chairmen of the Senate and House armed services committees, have proposed at least trying to get closer to Gates’s levels, calling for defense spending of $577 billion in 2016.

The fact that they face a steep uphill battle to get even that lower number passed by a Republican-controlled Congress says a lot — about Republican hypocrisy. Republicans may be full-throated in denouncing Obama for weakening the nation’s security, yet when it comes to paying for the foreign policy that all their tough rhetoric implies, too many of them are nowhere to be found.

At least Paul is consistent. He wants a smaller foreign policy and favors a smaller defense budget to pay for it. But what about those who claim they want a stronger foreign policy? Unless all their tough talk is hot air, they will need to cast votes to end the sequester and approve an increase in the defense budget. The editorial writers and columnists who have been beating up Obama and cheering the Republicans need to tell those Republicans, and their own readers, that national security costs money and that letters and speeches are worse than meaningless without it. And those calling for a tougher approach as they run for president need to say loudly, and frequently, while traveling through Iowa and New Hampshire and Florida, that a central plank of their candidacy, and a central goal of their presidency, will be breaking the sequester and increasing spending on defense.

Many people across the country won’t like hearing any of this. It will annoy the part of the Republican base that wants to see the government shrink, loves the sequester and doesn’t care what it does to defense. But leadership occasionally means telling people what they don’t want to hear. Those who propose to lead the United States in the coming years, Republicans and Democrats, need to show what kind of political courage they have, right now, when the crucial budget decisions are being made. And for those who decide to play it safe — well, let’s just say we won’t have to throw any cheese on the floor.