Graham is running in an increasingly crowded field as billionaire Jeff Greene jumped in the Democratic primary earlier this month. Other candidates include Levine, Tallahassee Mayor Andrew Gillum and Central Florida businessman Chris King.
The move comes as no surprise as Grimsley led the Senate Agriculture Committee in this year’s session.
Harris insisted that the stakes are high in the Sunshine State with control of the Senate at stake in Florida.
More than a third of likely Republican primary voters--34 percent--remain undecided.
Despite the endorsement, Manjarres does not have an open shot at the Republican nomination.
Pundits from across the nation consider this South Florida congressional race as a prime opportunity for the Democrats to flip a seat currently held by a Republican.