WASHINGTON -- Vice President Joe Biden is stepping up his efforts to help President Barack Obama win re-election, kicking off a series of speeches in states critical to the Obama campaign.

Biden will speak at four events in the coming weeks on key issues in the presidential campaign, including an address next week in Ohio, a campaign official said Tuesday. The official spoke on condition of anonymity to discuss campaign strategy.

The vice president has been a top surrogate for Obama, appearing at fundraisers around the country and courting voters in battleground states like Ohio, Pennsylvania and New Hampshire. The speeches are expected to mark a more pronounced role by Biden in the campaign as Republican presidential contenders compete in primary contests this spring.

Biden has helped the Obama campaign's outreach to white working-class voters in Ohio, Pennsylvania and elsewhere and to Jewish voters in Florida, a key group for Democrats. He is a frequent contact for organized labor, another important part of the Democratic base.

In the upcoming speeches, Biden is expected to offer a rebuttal to months of criticisms from Republicans in primary states while outlining some of the issues expected to play a major role in the campaign. Republicans have repeatedly accused Obama of mishandling the economy, arguing that the president's policies have made the recession worse.

On the night of the New Hampshire primary in January, Biden addressed party loyalists, defending Obama's record in the first-in-the-nation primary state. He told Democrats gathered at house parties that, in the next four years, "we're going to have an opportunity to really do the things we came to do and do it without the kind of recalcitrant interference we've had."

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