Rick Santorum and Mitt Romney. (Getty Images)
Washington, DC (written by Catalina Camia/USA Today) -- Rick Santorum tonight finally endorsed Mitt Romney for president, pledging to help his ex-rival defeat President Obama in November.
"The task will not be easy. It will require all hands on deck if our nominee is to be victorious," Santorum said in an e-mail to his supporters. "Governor Romney will be that nominee and he has my endorsement and support to win this, the most critical election of our lifetime."
The late-night e-mail comes about a month after the former Pennsylvania senator suspended his campaign, which cleared the way for Romney to be the Republican nominee. With the exception of Ron Paul, who continues to campaign, all of Romney's ex-rivals have now endorsed the presumptive GOP nominee.
Romney vs. Santorum was at times a bitter rivalry, marked by stinging attacks. Santorum had charged that Romney wasn't an authentic conservative, and was "uniquely disqualified" to go up against Obama because he signed a Massachusetts health care law that was similar to one pushed by the Democratic president.
They had a face-to-face meeting on Friday to discuss Santorum's concerns, including how Tea Party supporters and social conservatives -- who were at the heart of his primary victories in 11 states -- would be included in the campaign.
In his e-mail, Santorum said his one-on-one session with Romney was important to "assess Governor Romney's commitment to addressing the issues most important to conservatives, as well (as) his commitment to ensuring our appropriate representation in a Romney administration."
On the issue of health care, Santorum conceded he now has " no doubt" that the former Massachusetts governor will work to repeal the law he derides as "Obamacare" and "replace it with a bottom up, patient, not government-driven system."
(Contributing: Jackie Kucinich)