WASHINGTON (AP) — Mitt Romney padded his delegate count on the biggest night of the GOP presidential primary season but Rick Santorum demonstrated enough strength to ensure that there's more convulsion ahead as Republicans struggle to settle on a candidate to take on President Barack Obama.

Super Tuesday gave Romney a narrow victory in pivotal Ohio, a home-state win in Massachusetts, and triumphs in Idaho, Vermont, Alaska, and Virginia. But it was no knock-out punch.

Santorum, for his part, won Oklahoma, Tennessee and North Dakota, and Newt Gingrich picked up his home state of Georgia.

"This was a big night tonight," Santorum said. "We have won in the West, the Midwest and the South, and we're ready to win across this country."

The split decision refreshed questions about Romney's appeal to conservatives in some of the most Republican states in the nation. The best-funded and best-organized of the four Republican candidates, Romney vowed to press on.

"Tomorrow, we wake up and we start again," he told supporters. "And the next day, we'll do the same. And so we'll go, day by day, step by step, door by door, heart to heart."

House Republican Leader Eric Cantor of Virginia, a Romney supporter, said Wednesday that Romney's claim to the nomination is inevitable, adding that Santorum and Gingrich "have not demonstrated an ability to do what needs to be done." But in a morning interview on CBS "This Morning," Cantor acknowledged there is still plenty of ongoing debate in "a robust party with many ideas."

Obama chose the busiest day of the GOP race to speak from the presidential bully pulpit, where he dismissed the Republicans' almost constant criticism of his administration.

"Those folks don't have a lot of responsibilities," Obama said in a White House news conference. "They're not commander in chief."

Gingrich's win in Georgia, which he represented for several terms in Congress, was his first victory since he captured the South Carolina primary on Jan. 21. The former House speaker said it would propel him on yet another comeback,

Texas Rep. Ron Paul, still in search of his first victory of the nomination battle, had pinned his hopes on winning Idaho and Alaska but fell short in both.

Ohio was the marquee matchup, and for good reason. No Republican has won the presidency without carrying the state in the general election. It was a second industrial-state showdown in as many weeks between Romney and Santorum and drew the most campaigning and television advertisements of the 10 Super Tuesday states.

With 99 percent of Ohio precincts reporting, Romney had 38 percent to Santorum's 37 percent, an uncomfortably close margin for a candidate who had spent nearly four times as much money as his rival in the state.

Romney spent $1.5 million in television advertisements and Restore Our Future, a super PAC that supports him, spent an additional $2.3 million. Santorum and Red, White and Blue, a super PAC that supports him, countered with about $1 million combined, according to information on file with the Federal Election Commission.

There were primaries in Virginia, Vermont, Ohio, Massachusetts, Georgia, Tennessee and Oklahoma. Caucuses in North Dakota, Idaho and Alaska rounded out the contests. In all, 419 delegates were at stake across the 10 states. Romney picked up at least 212 delegates during the night; Santorum got 84, Gingrich 72 and Paul at least 22.

That gave the former Massachusetts governor 415, more than all his rivals combined. Santorum was second with 176 delegates, Gingrich had 105 and Paul had 47. It takes 1,144 delegates to win the nomination at the Republican National Convention in Tampa, Fla., this summer.

In interviews across all of the primary states, Republicans said the economy was the top issue and a candidate's ability to defeat Obama was what mattered most as they cast their votes.

Ohio Republicans were sharply divided, according to the popular vote and interviews with voters as they left polling places. Santorum triumphed over Romney among Ohioans with incomes under $100,000, while Romney won among those with six-figure incomes and up. Romney won among working women; Santorum won among women who do not work.

Santorum also was preferred by the half of the electorate that is born-again, while Romney was the favorite among those who were not.

The race moves to contests in Kansas, the U.S. Virgin Islands, Guam, Alabama, Hawaii, Mississippi and Missouri. Voting in Puerto Rico, Illinois and Louisiana rounds out the nomination schedule for March.