MILWAUKEE (AP) -- Republican front-runner Mitt Romney and President Barack Obama are trading jabs even before Republicans vote in their latest presidential primaries.

It's a sign that both sides believe the race to decide who will oppose Obama is coming to a close.

With GOP primaries Tuesday in Wisconsin, Maryland and the District of Columbia, Romney is set to hold one campaign event before an election night party in Milwaukee. He spent the weekend campaigning across Wisconsin, working to win yet another big industrial state that rival Rick Santorum has been counting on to keep his flagging candidacy alive.

Obama's re-election campaign is running a new TV ad in five swing states attacking Romney by name for the first time -- as a backer of Big Oil amid high gasoline prices.

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