President Obama spoke this morning at American University on the need for comprehensive immigration reform. The president deserves credit for turning his attention to a thorny problem that desperately needs action from Congress, but the speech failed to hit at least one important note.

While the president called for comprehensive reform, he neglected to advocate the expansion of legal immigration in the future through a temporary or guest worker program for low-skilled immigrants. Even his own Secretary of Homeland Security, Janet Napolitano, has said such a program is the necessary “third leg” of immigration reform, the other two being legalization of undocumented workers already here and vigorous enforcement against those still operating outside the system.

As I’ve pointed out plenty of times, without accommodation for the ongoing labor needs of our country, any reform would repeat the failures of the past. In 1986, Congress passed the Immigration Reform and Control Act, which legalized 2.7 million workers already here illegally, while beefing up enforcement. But without a new visa program to allow more low-skilled workers to enter legally in future years, illegal immigration just began to climb again to where, two decades later, we are trying once again to solve the same problem.

On the plus side, President Obama reminded his audience of the important role immigrants play in our open and dynamic country. And he rightly linked immigration reform to securing our borders:

“[T]here are those who argue that we should not move forward with any other elements of reform until we have fully sealed our borders. But our borders are just too vast for us to be able to solve the problem only with fences and border patrols. It won’t work. Our borders will not be secure as long as our limited resources are devoted to not only stopping gangs and potential terrorists, but also the hundreds of thousands who attempt to cross each year simply to find work.

Unfortunately, given the political climate in Washington, an election looming only four months away, and the president’s unwillingness to press for an essential element of successful reform, the illegal immigration problem will still be on the agenda when a new Congress comes to town in 2011.