John Sides summarizes the political science research on the question. In short:
First, the president’s ideas have at least some support already. If they didn’t, he probably wouldn’t have given the speech. Second, as the political scientist Jonathan Bernstein notes, the speech thus serves not so much to persuade lots of recalcitrant voters or members of Congress, but more to signal the President’s intention to push for these policies and, equally if not more important, to bargain about these policies. In other words, the speech, whatever its tone, was not laying proposals that are set in stone. Expect the speech simply to spawn additional debate and negotiation. If the end result is a bill on the president’s desk, we’ll have an excellent example of how presidential leadership really works. It’s not about magic words or eloquent moments. As Edwards said, it’s about facilitating change.
