(CNN) - New Jersey Gov. Chris Christie penned a fundraising e-mail Sunday to help Delaware Rep. Mike Castle fend off Tea Party insurgent candidate Christine O'Donnell in that state's Senate race.
"I know that Mike Castle agrees with what I've been doing in New Jersey since taking office in January: controlling spending, balancing the budget, reducing the size of government and creating an environment that allows our small businesses to thrive and grow," Christie wrote.
"He is the Republican that Delaware - and our country - needs in the United States Senate, and he is the only candidate in this race that can put this seat in the Republican column in November," he added.
Christie endorsed Castle at the University of Delaware - they both graduated from UD - on September 2.
Castle is vying with O'Donnell for the Senate seat vacated by Vice President Joe Biden.
While Castle has the backing of the GOP establishment - which has been fighting hard on his behalf - O'Donnell has received endorsements from leading conservatives such as Sarah Palin and South Carolina Sen. Jim DeMint.
Delaware's Senate primaries will be held on Tuesday.
–CNN Deputy Political Director Paul Steinhauser contributed to this report