We ask an awful lot of our presidential candidates. In addition to being forced to shake a million hands, beg for money, and cram any fried foodstuff right into their mouths, they're supposed to have opinions and ideas about everything. As soon as something important happens in the United States or anywhere else, in short order we expect them to have a "plan" to deal with it, to assure us that once they take office, the problem will be solved forthwith.

A couple of weeks ago, ISIS was a serious challenge the next president will have to deal with, but in the wake of the attacks in Paris, candidates are now expected to have an ISIS plan, a specific set of actions they'll take that will eliminate the terrorist group once and for all. Not everyone has come up with one yet, but what we've seen so far is not going to inspire a whole lot of faith that ISIS's days are numbered come January 2017.

Consider, for example, Marco Rubio, the establishment's golden boy and one of the "serious" GOP candidates. When it comes to foreign policy in particular, people will look to Rubio, since by virtue of his seat on the Senate Foreign Relations Committee he's better informed than most of his primary competitors. Rubio delivered his plan to defeat ISIS last week, and it's a remarkable document. Let's walk through its main points.

Rubio begins with the requisite statement of steely resolve: "When I am president, what I will do to defeat ISIL is very simple: whatever it takes." Inspiring! Then he dives into the details. "First, I would protect the homeland by immediately stopping the flow of Syrian refugees into the United States," he says. I won't bother going over again how wrong it is to think that stopping Syrian refugees will protect us from an attack, but we can at least all agree that doing so certainly won't help "defeat" ISIS.

"Next, I would reverse defense sequestration so we have the capabilities to go on the offense against ISIL," Rubio says. This is equally silly. You can argue that the budget cuts forced by sequestration are a bad thing, but the reason we haven't yet banished ISIS from the earth isn't that our defense budget is too skimpy. It's not like the chairman of the Joint Chiefs is saying, "Mr. President, we could take ISIS out and bring a peaceful, democratic government to that area, but we can't do it without more tanks and helicopters — and I just don't have the money." Our resources are more than ample for whatever military action we might want to take.

Next, Rubio says "I would build a multinational coalition of countries willing to send troops into Iraq and Syria to aid local forces on the ground." Also, "I would demand that Iraq's Shiite-dominated government grant greater autonomy to Sunnis, and would provide direct military support to Sunnis and the Kurds if Baghdad fails to support them. I would back those demands with intense diplomatic pressure and the leverage of greater American military assistance to Iraq." So that's a mix of things the Obama administration is trying to do (though somehow Rubio would manage to convince other countries to put in troops where Obama hasn't been able to; maybe Obama's diplomatic pressure hasn't been "intense" enough), plus something that sounds like he wants to set up an independent Sunni quasi-state within Iraq, like what the Kurds have. That's...interesting. Shouldn't be any complications there.

And finally, "Cutting off oxygen to ISIL also requires defeating Assad in Syria. I would declare no-fly zones to ground Assad's air force and coalition-controlled 'safe zones' in the country to stop his military." If you read that without knowing anything, you might think Rubio believes that Assad is supporting ISIS and not fighting it. But anyhow, he'll just "defeat Assad," whom we're not actually fighting at the moment. Does that mean an invasion? If not, what? And "safe zones" sound nice, but how many tens of thousands of American troops would be required to create and maintain them?

Now keep in mind: This collection of ideas ranging from the irrelevant to the ridiculous is the best plan the GOP's best foreign policy candidate can devise.

The problem isn't that Marco Rubio is some kind of idiot, even if you'd be tempted to conclude that upon reading his "plan." The problem is that ISIS presents an unusually difficult challenge, where every possible course of action is either foreclosed before it begins or brings huge complications along with it. That's why when Hillary Clinton — who has more foreign policy experience than all the Republican candidates put together — gave a speech last week outlining the course she'd like to follow on ISIS, it was terribly frustrating, in many ways more hope than plan. Clinton at least acknowledges the complexity of the situation — for instance, our ally Saudi Arabia isn't helping us fight ISIS, while our adversary Iran is, all while the two countries wage proxy battles against each other. If the next president can untie that knot, it would be a wonder.

Presidential candidates never acknowledge that some challenges are so difficult that success is uncertain at most. They don't say, "Boy, this one's a doozy, but I'll do my best." They say that if they're elected, all our problems foreign and domestic will be swept away. It's when they try to explain exactly how they're going to get there that the future doesn't look so bright.