Joseph Biden wants the United States to intervene with military force to stop the genocide that he and George W. Bush say is going on in Darfur.

“We should enforce a no-fly zone, impose multilateral sanctions through the U.N., lead negotiations among all the parties for a lasting peace settlement, find the forces for a peacekeeping mission and, if necessary, commit U.S. troops on the ground,” he said in a statement.

Biden is chairman of the Foreign Relations Committee and a candidate for president, and he deserves to be taken seriously. My questions for him: How many U.S. troops would you put “on the ground”? For how long? What is your strategy for winning? And do you have an exit strategy absent victory?

These are questions that many people, including Biden, have asked quite reasonably about Bush’s decision to intervene with military force in Iraq.

Biden acknowledges that there are “logistical obstacles and humanitarian concerns involved in this approach.” No kidding. Darfur is far distant from U.S. bases or the open sea, it has little physical infrastructure, and the Sudanese government and some indigenous peoples would likely be hostile.

Russ Feingold, Biden’s colleague in the Senate who thought about running for president but decided not to, takes another view. He reacts positively to Bush’s “long overdue” strengthening of sanctions on the Sudanese government, but in his view it is not enough.

“In order for the initiatives announced today to be effective,” he says, “the administration must redouble its diplomatic efforts at the United Nations, and in particular with reluctant Security Council members, to ensure these initiatives are complemented by similar multilateral measures. This administration must work in concert with the international community if targeted sanctions and economic pressure are to have any meaningful impact in reversing the humanitarian crisis and ending the genocide in Sudan.”

My questions for him: Why do you suppose that redoubled diplomatic efforts will do anything to persuade China, which buys oil from Sudan, to cooperate? What do you do if it continues to be impossible to get the Security Council to authorize sanctions? What steps are you prepared to take to enforce sanctions?

Biden at least realizes that in a less-than-perfect world, with many evil persons doing evil things, military action is sometimes necessary to stop them. Feingold seems to assume that diplomatic suasion is all that is needed, at least for now. But their two different approaches have two things in common.

One is that it is better to intervene where we don’t have major security interests than where we do. Feingold opposed from the beginning our intervention in Iraq, and Biden, who voted for the Iraq war resolution, now wants us to move toward withdrawing. Yet Iraq is in a critical part of the world for us, and a speedy withdrawal from Iraq would be, as the Iraq Study Group concluded, a terrible blow to our national interest.

Any intervention in Darfur, through sanctions or military force, would be strictly humanitarian, like our interventions in Bosnia and Kosovo in the 1990s. We had little in the way of national security interests there – local civil wars were not able to embroil Europe in crisis. But Bill Clinton decided to intervene militarily, and most Democrats supported him. They approved our intervention there precisely because it was humanitarian and not in pursuit of security interests.

The other thing they have in common is a preference for multilateral over unilateral intervention. Biden wants the United Nations and the African Union to be involved, although the African Union force has so far been ineffective and the record of U.N. forces in Africa is abysmal. Any major military force is going to be a largely American force, for the simple reason that the United States has most of the world’s out-of-area military capacity. Feingold thinks sanctions will be stronger if they’re endorsed by the U.N. Security Council and the “international community.” That’s true, but it probably leaves the people of Darfur with a long time to wait.

Democrats like Biden and Feingold seem to want the United States to abide by children’s playground rules. It’s selfish when you intervene to help yourself, but it’s acceptable when you intervene to help others. It’s egotistical when you do things alone, but it’s commendable when you play well with others. But those rules aren’t much help when a child molester stalks the playground. Sometimes you have to act alone and act out of self-interest to prevent evil people from doing evil things.