U.S. Republican presidential candidate Rick Santorum is riding high Wednesday after nominating contest victories in three states, which have raised questions about the front-runner status of former Massachusetts governor Mitt Romney.

The socially conservative Santorum is campaigning in Texas Wednesday after winning Tuesday's caucuses in Minnesota and Colorado and the primary in Missouri. The wins raise pressure on Romney and emphasize his struggle to gain the support of the conservative Republican base.

Tuesday's shake-up in the battle to take on Democratic U.S. President Barack Obama in November also dealt a blow to former House of Representatives speaker Newt Gingrich, who had previously been seen as the top alternative to Romney. Gingrich finished a distant third in Colorado and a distant fourth in Minnesota. He was not on the ballot in Missouri.

Gingrich is now focusing his attention on Ohio, which has begun early voting ahead of its primary on March 6, when about 10 states hold their nominating contests in an event known as “Super Tuesday.”

Romney is also campaigning in a Super Tuesday state Wednesday, with events in Georgia. Despite his losses, Romney told a rally in Colorado Tuesday night that he still expects to be the Republican nominee.

Meanwhile, Texas Congressman Ron Paul celebrated his second place finish in Minnesota. Paul has no campaign events planned Wednesday.

With most of the Minnesota returns counted, Paul took 27 percent of the vote behind former Pennsylvania senator Santorum, who had 45 percent. Romney finished a distant third with 17 percent.

Santorum also pulled off an upset victory over Romney in the Colorado caucuses, winning more than 40 percent of the vote, compared to Romney's 35 percent.

The outcome was especially disappointing for Romney considering he won both Colorado and Minnesota in the 2008 Republican race.

In the Missouri primary, with all the votes counted, Santorum won 55 percent of the vote, while Romney came in second with 25 percent and Paul finished third with 12 percent.

A total of 70 delegates are up for grabs in Colorado and Minnesota, although they will be awarded later at district and state conventions. Missouri's primary is non-binding, with no delegates at stake.

To be selected to face Mr. Obama in the November general election, a Republican needs to have the support of 1,144 delegates at the Republican nominating convention in Florida in August.