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.

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