After 14 years in Congress, Paul Ryan has become the Republican Party’s brand name for conservative economic policies: Low taxes, reduced spending and entitlement reform, all wrapped into a GOP budget plan that bears his name.

As he prepares to give the most important speech of his career Wednesday night as the Republican nominee for vice president and introduce himself to millions of Americans, the 42-year-old congressman from Wisconsin must sell voters on a different proposition: His own readiness to become president of the United States.

“Can he step in and do the job? That’s really the only thing that matters,” said Romney pollster Neil Newhouse.