Joe Biden told us that one of our adversaries deliberately would test Barack Obama early in his presidency. He was right, but they didn't wait until after his inauguration. No sooner had Obama become the president-elect than Russian President Dmitri Medvedev threw down the gauntlet. If the US went ahead with its plan for a missile-defense system in Poland and the Czech Republic, Russia would place nuclear-tipped missiles on its border with Poland. If, however, the US ends its plans, Russia is ready to respond positively.

So what’s the new president to do? Now, even if Obama had planned to back out of the agreement with the Poles and the Czechs, he has to be extremely careful how he does it or he’ll look like he’s conceding to Medvedev’s demands. That would give friends and foes around the world the impression he’s weak and invite others to test him.

Nevertheless, if Obama is determined to reverse Bush’s policy on missile defense in Europe, he can certainly find a way to do it. At this point his intentions aren't clear. Although he said on the campaign trail that we needed defense against missiles from Iran, he also said in a campaign ad that he would cancel “unworkable” missile defense programs and save billions of dollars. He can wait a decent interval, then say he just doesn’t have confidence in the technology and, in the middle of a global financial crisis, it’s costing the taxpayers billions of dollars the country can’t afford.

He can draw on arguments used by those who oppose our own missile defense program to bolster his case. They say it’s a defense against the wrong threat. It’s much easier, they argue, for terrorists to smuggle a suitcase with a nuclear, biological, or chemical device into a country, especially in Europe, with its porous borders. Why waste time, money, and effort defending against ballistic missiles? We should use those resources to develop programs and systems that improve our defenses against surreptitious terrorist threats.

French President Nicolas Sarkozy added weight to this argument last week. Following a meeting with Medvedev, Sarkozy said the next American administration’s plans for a US missile shield in Eastern Europe are misguided and won’t make the continent a safer place. He chided Medvedev as well for his statements, but Sarkozy reflects an opinion held by some of our NATO allies. A missile defense system in Poland and the Czech Republic, even though it's aimed at the Middle East, not Russia, only forces the Russians to deploy missiles to counter it. They deploy their missiles and we have to deploy our missiles to counter theirs. One thing leads to another and before you know it we have Cold War II.

All these arguments contain an element of truth. Some people find them compelling. And if President Obama chooses, he can use them to rationalize backing away from the European missile-defense program. The majority of Americans aren’t likely to disagree with him.

Yes, the European program is expensive. There’s the cost of the program itself and the aide we promised the Poles and the Czechs in order for them to agree to it. But Iranian ballistic missile programs present a serious threat to Europe and US interests in Europe. One of Iran’s principal reasons for pursuing them is to intimidate the Europeans. Once they acquire a nuclear weapon, the intimidation factor of those missiles increases dramatically. Ending the program will only embolden Iran further. Can we afford to take that risk?

Backing out of our missile-defense commitment to Poland and the Czech Republic, which they readily entered into when Russia invaded Georgia, only encourages Moscow to put more pressure on its former satellite states. Medvedev says Russia is ready to respond positively, but at what further cost? What will they demand next?

Yes missile defense technology is on the cutting edge, and it’s not perfected yet, but we’ve finally reached the point that Ronald Reagan only dreamed about when he announced the “Star Wars” program in the mid-1980s. Missile defense is no longer just a theory. We’ve proven it works. We have a working, if limited, missile-defense system of our own. Countries like Israel, Japan, and Taiwan understand that and they’re anxious to have missile defense systems of their own.

Yes, terrorists can smuggle a suitcase with a nuclear, chemical, or biological weapon in it across international borders. But it’s not all that easy, and we’re making it harder all the time. We can detect, intercept, and prevent terrorist attacks after they’ve been launched and before they strike. Without missile defense, once that missile leaves the launch pad, it’s practically a certainty it’s going to strike its target. Whether your enemies are more likely than not to use a terrorist attack than a ballistic missile doesn’t mean you don’t defend against both.

Yes, if the Russians choose to make it so, the European missile-defense program can be somewhat destabilizing. But it doesn’t have to be. Washington has already extended the olive branch to Moscow. It’s offered to share its missile-defense technology with Russia. They’re not upping the ante on missile defense because they feel threatened by it. They’re doing so because they resent the US presence in their former sphere of influence and they want to roll it back. Empowered by new oil wealth, somewhat diminished in the current crisis, they seek to regain much of what was lost when the Soviet Union fell.

President Obama should stand firm on our agreements with the Poles and the Czechs. To do otherwise will leave Europe and US interests in Europe vulnerable to Iran’s developing ballistic missile capabilities. It will further embolden Iran, Russia, and others to challenge US influence. Candidate Obama said he wanted to sit down and talk to our adversaries. No doubt he’ll have an early opportunity to met with Medvedev and Vladimir Putin, the man who really runs Russia. Let them look Obama in the eye and understand he won’t be bullied or pushed around. We’ll all be a lot safer when that happens.