If the economy doesn't improve, President Obama will be in re-election trouble, especially if he faces Mitt Romney or Rick Perry, two Republicans with executive experience who are stressing jobs as an issue. But some Republicans are still unhappy with the prospect of one of those two winning the nomination and are trying to persuade House Budget Committee Chairman Paul Ryan to run. That could be a mistake. Ryan is the one person most associated with the fight to reduce the size of federal government, and that could give Obama a chance to change the focus of the campaign: