Sen. Ted Cruz (R-TX) stated that the Democrats’ and media’s criticisms of Marco Rubio, including their attacks on him for drinking water during his State of the Union response, are motivated by fear of Rubio’s appeal because he is Hispanic. 

I think Democrats and the media are afraid of Marco Rubio because he is a smart, intelligent, conservative Hispanic. And they are looking for any excuse they can to attack him, because that threatens them... Look, he took a drink of water in a speech. And it dominated the news for days with one network saying it was a career ender.

Cruz continued, "I think the Democrats view Marco Rubio as a particular threat because of his background, his life story. I think it they believe it is in their interest to inflict as much damage as possible and blow things wildly out of proportion.”

Rubio’s ascendancy within the GOP has been noted by Time magazine, which ran a cover story that featured Rubio as "The Republican Savior" and called him the "great Hispanic hope of the Republican Party." 

The 2012 election revealed Hispanics voted in droves for Barack Obama, and Rubio is a threat to Democrats to help the GOP appeal to those voters.