By TOM RAUM, Associated Press
Mitt Romney may get a boost from his choice of Wisconsin Rep. Paul Ryan as his running mate — and also from the upcoming Republican National Convention in Tampa, Fla.
That would be welcome to a campaign that saw slippage to President Barack Obama by several percentage points in polls before Saturday's Ryan announcement.
Positive bumps are common in presidential politics. But it's just as common for them to fade, sometimes quickly.
Sen. John McCain got a nice spike from his selection of Alaska Gov. Sarah Palin followed immediately by an upbeat 2008 Republican convention in St. Paul, Minn. It allowed the GOP nominee to draw even with Obama in some polls heading into the fall campaign season.
But the gain was fleeting.
Controversy quickly arose over Palin's qualifications. And the ticket suffered from McCain's erratic response to September's financial meltdown, including his off-key claim that "all the fundamentals are fine."
Some polls show a divided initial response to Ryan's selection. They also suggest voters don't know much about him, despite his prominent role in Washington as the architect of conservative GOP budgets.
Both sides are now scrambling to define him for voters. Democrats paint a "right wing ideologue" whose budgets would gut Medicare and reward the wealthy with tax breaks at the expense of the middle class. Newly energized Republicans see him as a spirited champion of conservative values who would help rein in federal spending.
"If there is a bump, it's likely to be short-lived," said pollster Andy Kohut, president of the Pew Research Center, noting the Democratic convention closely follows the GOP one.
All four candidates campaigned Tuesday in battleground states.
Obama continued his bus trip across Iowa while Romney campaigned in Ohio. Ryan stumped in Colorado and Nevada, Vice President Joe Biden in rural southern Virginia.
Follow Tom Raum on Twitter: http://www.twitter.com/tomraum. For more AP political coverage, look for the 2012 Presidential Race in AP Mobile's Big Stories section. Also follow https://twitter.com/APCampaign and AP journalists covering the campaign: https://twitter.com/AP/ap-campaign-2012
With 84 days left until Election Day, here are insights into today's highlights in U.S. politics
Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.