Mitt Romney’s grip on the Republican nomination tightened last night, with convincing victories in Wisconsin, Maryland and Washington, D.C. Romney’s win in Wisconsin can be chalked up to strong performances across some of his most reliable voting groups, including electability and upper-income voters. Here are a few other interesting results from the exit polls.

See the full Wisconsin and Maryland exit poll results in the Post’s Republican Primary tracker..

Spoiler alert - A significant number of Democrats and independents joined Republicans in voting for the GOP nominee in Wisconsin, but their participation didn’t help the front-runner. Romney beat Rick Santorum by 50 to 37 percent among self-identified Republicans, but topped him narrowly among independents and lost Democrats by 21 points. Independents and Democrats upped their share of the GOP primary electorate to 30 and 11 percent, respectively, from 23 and 5 percent in 2008.

In another sign of the unusual role that Democrats played in the Wisconsin primary, about seven in 10 disapprove of Republican governor Scott Walker. Among Republicans, 92 percent approve of him as do 70 percent of independents. 

Health care doesn’t hurt Romney: Thirty-six percent of Wisconsin primary voters picked Romney as the candidate they trust most to handle health care policy. He edges out Santorum, whom 31 percent pick as the best to handle health care. Santorum has hammered Romney for his support of health care reform in Massachusetts, saying his past makes him ill-suited to challenge Obama on the law he signed in 2010.

Romney invited to a tea party - Romney had two of his best showings so far among strong tea party supporters on Tuesday. He won 50 percent of this group in Wisconsin and 46 percent in Maryland, much better than his 33 percent average across all states this year. The only states where he won more support were Massachusetts — where he was governor — and Virginia, a two-man fight with Ron Paul.

Romney has struggled for acceptance among this core Republican group, losing them to Santorum or Newt Gingrich in a string of contests since Super Tuesday.

These are preliminary results of a poll of 2,095 Republican voters as they exited primary voting places in Wisconsin on April 3, 2012. Typical results have a margin of sampling error of four percentage points; error is higher for subgroups. The poll was conducted by Edison Media Research for the National Election Pool, The Washington Post and other media organizations.