Click here to watch "America's Leadership."

Coinciding with his speech today on Iraq and national security, Barack Obama is releasing a new TV ad discussing his vision of America's role on the international stage.

In "America's Leadership" (subscription), Obama expresses his intent to "restore America's leadership in the world," striking a note reminiscent of President Reagan's "shining city on a hill" message in the 1980s. "We are a beacon of light around the world," he tells a small group of voters in a town hall meeting. "At least that's what we can be again. That's what we should be again."

He goes on to identify what he considers to be the "single most important national security threat that we face" -- "nuclear weapons falling into the hands of terrorists." "What I did was reach out to Senator Dick Lugar, a Republican, to help lock down loose nuclear weapons," Obama says, emphasizing his ability to work across the aisle on a topic he is passionate about.

The spot will run in the 18 states previously targeted for Obama's first set of general election TV ads, including Florida, Iowa, Indiana, New Hampshire, New Mexico, Ohio, Pennsylvania and Virginia.