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Both candidates have been working to build their resumes before the 2016 primaries. Rubio has served as an integral part of immigration reform efforts on Capitol Hill, while Paul memorably led a talking filibuster to protest the Obama administration's drone policy. Both have booked fundraising events in early voting states later this year, and both delivered responses to President Obama's State of the Union in February.

Still 28 percent of Americans said they did not know who Paul was, and 38 percent said the same of Rubio. Moreover, four in 10 Hispanic voters said they did not know or did not have an opinion of Rubio.

For Democrats, former Secretary of State Hillary ClintonHillary Rodham ClintonManafort to share notes from Russian meeting with Senate probe: report Scarborough to Trump: Switch cable news to ‘SportsCenter’ Ex-Bush ethics lawyer: Trump calling for Clinton to be prosecuted is an ‘impeachable offense’
 MORE continues to be the prohibitive favorite to win the nomination were she to enter the race. Of those surveyed, 88 percent had a favorable impression of Clinton.