Mitt Romney set a record with at least two of Tuesday's primary wins, but it's an achievement the presumptive Republican nominee probably won't be bragging about.

The former Massachusetts governor won Delaware with 56 percent of the vote and Pennsylvania with 58 percent. According to University of Minnesota political scientist Eric Ostermeier, that marks the first time that a presumptive GOP nominee has failed to reach the 60 percent mark in a contest conducted after his last major challenger exited the race.

"While Romney avoided the embarrassment of winning with a mere plurality, never has a presumptive nominee won a primary contest with such a low level of support at this stage of the race with his chief challenger no longer actively campaigning," Ostermeier writes at Smart Politics, the university's political site. Smart Politics reviewed Republican primary election data since 1972.

While the Romney campaign insists a win is a win, Romney's below-60-percent victories in Delaware and Pennsylvania come after months of questions about whether the ex-governor will be able to unite Republicans around his candidacy.

At the same time, Romney's somewhat lackluster showings came in states where his GOP rivals made their last campaign pushes. Newt Gingrich made Delaware the last stand of his 2012 bid—ultimately scoring 27 percent. In Pennsylvania, 41 percent of voters opted to cast ballots for other candidates: 18 percent voted for native son Rick Santorum, who dropped out earlier this month; 13 percent supported Ron Paul; and 10 percent voted for Newt Gingrich.

And voter turnout in the states was relatively light—perhaps given the expectations that Romney would emerge victorious.

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