Fred Barnes, writing in the Wall Street Journal:

After naming Paul Ryan as his running mate this month, Mitt Romney gave better speeches, especially when Rep. Ryan was at his side. Gov. Romney's poll numbers ticked up in Ohio and Virginia, both swing states. His online fundraising shot up like a geyser (68% of it coming from new donors). The Romney Facebook page added 510,000 friends in five days. Those are the most tangible signs of the Ryan Effect on the presidential campaign. Yet they are not the most important. Once Mr. Ryan entered the race, everything changed: the issues, the substance of the candidates' speeches, perceptions of Mr. Romney and President Obama, the role of a running mate. Never before has a vice presidential candidate become a central figure in a presidential race. There was no Gore Effect in 1992 or Cheney Effect in 2000. And never have a running mate's ideas become leading issues overnight, likely to dominate the campaign through election day. The Ryan Effect turned the race upside down. The thrust of Mr. Obama's bid for re-election had been maligning Mr. Romney and pandering to Democratic interest groups. Mr. Romney was concentrating on attacking Mr. Obama for the subpar economic recovery and weak job growth.

Whole thing here.