With Barack Obama leading in the polls, the last thing his campaign desired was a gift-wrapped issue handed to John McCain and the Republicans — particularly dealing with foreign policy.

So why did Mr. Obama’s running mate, Sen. Joe Biden, raise such an issue, namely the inevitability that one of this nation’s enemies quickly would test a President Obama? To be sure, Mr. McCain’s backers are pleased Mr. Biden explained with laser-like accuracy what might confront this nation. Still, one wonders why he said what he did. To wit:

“Mark my words,” Mr. Biden told a rally in Washington state, “it will not be six months before the world tests Barack Obama like they did John Kennedy. The world is looking ... Watch, we’re gonna have an international crisis, a generated crisis, to test the mettle of this guy ... I can give you at least four or five scenarios from where it might originate, and he’s gonna need help.”

A comparison and a contrast offer themselves. The comparison, obviously, was made by Mr. Biden himself. John F. Kennedy labored through a rocky start to his cold-war presidency, precisely because he was untested, and perceived as “intelligent” yet “weak” by America’s adversaries. Does this strike any present-day chords?

Mr. Kennedy met face-to-face with these enemies, as Mr. Obama has pledged to do, and was thoroughly steamrolled by Nikita Khrushchev. JFK admitted the Soviet leader “just beat the hell out of me.” The Soviets intensified their aggressive behavior, witnessed in the construction of the Berlin Wall and the precipitation of the Cuban Missile Crisis.

Such was the bitter fruit of a foreign policy grounded in “engagement,” or talks with enemies without “precondition.” Mr. Biden was spot-on in his dark foreshadowing of events to come. The world is still a dangerous place. With each election, our intractable foes want to know the lay of the land. They are eager to test the resolve of the free world’s new leadership, particularly a president untested in world affairs.

By way of contrast, as noted above, John McCain is a commodity better known in international circles. He’s been tested, not only in the crucible of war, but also, as the prime advocate and defender of the “surge” policy in Iraq, in the arena of world opinion. Our enemies would be less likely to probe his resolve or his willingness to react firmly and forcefully in a crisis.

As Pete Hegseth, the former Airborne officer now chairing Vets for Freedom, has said, “Most of us on 9/12 thought another terrorist strike would be inevitable — but it hasn’t happened.” And the reason is obvious: This nation reacted strongly in defense of liberty.

So why would America’s voters want to risk another attack, or even a “crisis” of some making, by ushering into office a new administration whose second-in-command freely admits its elevation to higher office would invite potential calamity?