Already the presumptive nominee, Mitt Romney could effectively shut out his remaining Republican presidential rivals in the next round of primaries Tuesday and emerge the clear rival to President Obama in November. 

The five-state set of primaries Tuesday became decidedly less interesting after Rick Santorum, Romney's top primary opponent, suspended his campaign earlier this month. But the low-key race could set the field for the general election. 

On the Democratic side, Obama is expected to formally clinch his nomination on Tuesday -- achieving the needed 2,778 delegates by the time polls close Tuesday night. Not that there was ever any doubt, as the Democratic primary was uncontested. 

On the Republican side, Romney has the opportunity Tuesday to sideline both Newt Gingrich and Ron Paul. While Romney will not be able to clinch the nomination outright -- he needs 1,144 delegates to do that, and will not reach that threshold Tuesday -- he could make it mathematically impossible in most scenarios for either of his two remaining opponents to reach that number. 

If both Paul and Gingrich perform poorly on Tuesday night, the number of delegates they each need to pick up to reach 1,144 will exceed the number left on the table, based on numbers in the Associated Press tally. 

Asked for comment on the looming contests, the Gingrich campaign gave no indication it was considering an exit from the race. 

"Gingrich is conservatives' last hope in this primary. He remains committed to the conservative cause and this election," spokesman R.C. Hammond said. 

The Gingrich campaign hopes the delegate numbers reported in the AP tally are fluid -- the campaign, for instance, challenges the awarding of all Florida's and Arizona's delegates to Romney despite their violation of party rules in holding early elections. 

The Gingrich campaign has also predicted it will do well in at least one of Tuesday's contests -- the primary in Delaware. The other primaries are being held in New York, Pennsylvania, Rhode Island and Connecticut, states thought to be friendly territory for former Massachusetts governor Romney. 

A total of 209 delegates are at stake. 

The latest AP tally puts Romney at 697 delegates, Gingrich at 137 and Paul at 67. Santorum had 269 delegates before he suspended his campaign. 

Romney has long been campaigning as a de facto general election candidate, focusing his stump speeches on Obama. He was glossing over his rivals even before Santorum dropped out. 

Gingrich, though, has continued to campaign. Despite a communication glitch that resulted in reports over the weekend that he was canceling a planned North Carolina trip, the campaign released a schedule on Saturday showing Newt and Callista Gingrich blanketing the state through the end of this week. North Carolina holds its primary May 8.