Costa won by just 4 points last year despite outspending his opponent by nearly $1 million, and the National Republican Congressional Committee has put the 16th and 21st districts atop its California target list as it seeks to stem the number of seats it stands to lose because of redistricting.
The Central Valley is a good place to start. A Field poll conducted last month found President Barack Obama with a 35 percent job approval rating there, and Valadao, a partner at the dairy farm his family has owned since 1974, said in an interview that the president and Democrats' representation of the area in recent years will be a boon for his campaign.
"The district in the last election showed us that the Central Valley is fed up with the other party," Valadao said. "They've been represented by them for the last 10, 20 years, and we're worse off than we've ever been."
Valadao won a Democratic-leaning Assembly district last year by 21 points, defeating a Democrat with a well-known name: Fran Florez, a former Shafter City Councilor and mother of state Senate Majority Leader Dean Florez. Dean Florez coincidentally was Rubio's mentor and was reportedly also considering running in the 21st, though no Democrat who spoke with Roll Call believed he would actually run.
Johnny Amaral, the longtime chief of staff to Rep. Devin Nunes (R-Calif.), recruited Valadao (who also is his cousin) to run in that race. After Valadao's big win in an Assembly district with a double-digit Democratic voter registration advantage, Amaral said Valadao now represents roughly two-thirds of a Congressional district that no Democratic incumbent wanted to run in.
"David's very popular, very well-liked, and he's working hard," Amaral said. "And we think he's going to be very well-positioned to win that seat and hold it."
Neither candidate has had a full three months of fundraising, but both said the third-quarter reports they file with the FEC this week will put them in a good position at the outset of the campaign. The new 21st is one of the biggest swing districts in the state — had it been in place the past two cycles, Obama would have won 51 percent in 2008, and in 2010, Gov. Jerry Brown (D) would have won by 4 points and Sen. Barbara Boxer (D) would have lost by 10 points.
"This is the district Costa thought he might lose a year ago, and it's changed but not really changed a lot," said Mitchell, a redistricting expert. "But in talking to people that are even on the Republican side, they feel that Rubio is a tough candidate to beat."
Former Sen. Scott Brown, R-Mass., candidate for U.S. Senate in New Hampshire, holds his hand over his heart during the singing of the national anthem as he waits to take the stage for his town hall campaign rally with Sen. John McCain at the Pinkerton Academy in Derry, N.H., on Monday, Aug. 18, 2014.