In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].

Washington (CNN) -- For both presidential campaigns, Republican Mitt Romney's choice of Wisconsin congressman and conservative star Paul Ryan as his running mate was like Christmas come early. Conservatives wanted one of their own on Romney's ticket and they got that in Ryan, who has emerged as their ideological leader on the Hill on fiscal and budget matters. The choice also helps satisfy Republican strategists who felt Romney needed to not only stress how President Barack Obama has failed in that role, but also better articulate what the GOP candidate would do if elected. "Ryan is a great choice. He energizes an already motivated party to a further degree and will help clarify the differing visions between the two campaigns for the country," said Phil Musser, a GOP strategist who in 2007 was a senior adviser to Romney's presidential campaign. "There are big choices, and in making the selection, Romney is showing that he believes America is ready for the choice."Both sides got what they wanted in Mitt Romney's choice of Paul Ryan as his running mateConservatives celebrate Ryan's selection; choice helps shore up some support for RomneyDemocrats quick to attack Ryan's selection as proof of Romney's conservative visionPolitical experts say both sides will battle over how to introduce Ryan to American public 
 Question:But even more troubling, Romney's unfavorable numbers were creeping up after weeks of attacks by the _ campaign and those supporting it.
Barack Obama