Monday was the last full day of campaigning by the GOP candidates before Tuesday's three primaries.
Mitt Romney's expected to win all three primaries Tuesday in Washington, D.C., Maryland and Wisconsin.
And Congressman Paul Ryan, who introduced him in Green Bay, said if that happens, the GOP campaign is effectively over.
Rick Santorum is keeping expectations low in Wisconsin, but raising them for home state Pennsylvania and its primary in three weeks, meaning, he's not quitting either.
Santorum, who frequently complains about negative ads, released a new one in Wisconsin that compares Romney to Obama.
For his part, Romney continued in general election mode, hammering President Obama and making no mention of GOP opponents, setting his sights on November.
Wins on Tuesday could put Romney about halfway to the number of delegates he needs for the nomination.