Former Republican presidential candidate Rick Santorum is urging his supporters to back Mitt Romney.

In a late-night email to his supporters, Santorum said despite his disagreements with Romney, "above all else, we both agree that President Obama must be defeated."

Santorum bowed out of the race last month after failing to win enough electoral votes to beat his rival.

At one point during the campaign, the former Pennsylvania senator said Romney was the worst Republican to beat the president.

Romney has since sought to assure Santorum of his conservative credentials.