Voting underway in Tuesday primaries

A patriotic voter in Green Bay, Wis. (Justin Sullivan / Getty Images)

March 24, 2014 2:02 PM PT

Mitt Romney looks for a sweep in Tuesday’s three Republican primaries -- Wisconsin, Maryland and the District of Columbia -- to tighten his grip on the party’s nomination.

People vote in Waukesha, Wis. (Scott Olson / Getty Images)

An election worker holds a roll of stickers at a polling place in Pewaukee, Wis. (Scott Olson / Getty Images)

A sign directs voters to a polling place in Derwood, Md. (Chip Somodevilla / Getty Images)

A sample ballot in Pewaukee, Wis. (Scott Olson / Getty Images)

Election workers help voters with a digital voting machine in Potomac, Md. (Chip Somodevilla / Getty Images)

Winifred O’Neill, 97, votes with some help from daughter Peggy in Frederick, Md. (Luis M. Alvarez / Associated Press)