(AP) - Mitt Romney tightened his grip on the Republican presidential nomination Tuesday night, sweeping primaries in Wisconsin, Maryland and Washington D.C., with time left over to swap charges with President Barack Obama. "Four more years?" Romney asked sarcastically of the president as supporters cheered him in Milwaukee. He said Obama was "a little out of touch" after spending four years surrounded by the trappings of power and had presided over near-record job losses as well as increases in poverty, home foreclosures, government debt and gasoline prices. The victories enabled Romney to pad his already-wide delegate lead over Republican rival Rick Santorum, who flashed defiance in the face of pressure to abandon his own candidacy in the name of party unity. Wisconsin was the marquee contest of the night, the only place of the three on the ballot where Santorum mounted a significant effort. Returns from 10 percent of the state's precincts showed Romney with 42 percent of the vote to 39 percent for Santorum, 11 percent for Ron Paul and 6 percent for Newt Gingrich.