Democrats are eager to portray these challenges as an indication that Republicans are spending more time fending off an insurgency from the tea party wing than preparing for the general election.
That Republican-on-Republican tension is evident with Senate Minority Leader Mitch McConnell's (KY) campaign. McConnell faces a primary challenge from Kentucky businessman Matt Bevin and has also taken criticism from the Senate Conservatives Fund. In response McConnell has called a recent Senate Conservatives Fund attack "profoundly stupid" and he also reportedly "lit into" a conservative challenger in Nebraska for his ties to the group.
A big exception to the safe Democratic nominations is the Hawaii Senate race. Sen. Brian Schatz (D) faces Rep. Colleen Hanabusa (D) in the primary, mainly due to the fact that Schatz was appointed by Hawaii Gov. Neil Abercrombie (D) despite deceased Sen. Daniel Inouye's (D) dying wish that Hanabusa should succeed him.
National Republican Senatorial Committee communications director Brad Dayspring said the reason some of the most high profile Democrats up for re-election this cycle aren't facing primary challenges from members of their own party is that it's hard to move farther to the left.
"Democratic Senators running for re-election are far outside the mainstream in their states and their liberal voting records show it," Dayspring wrote in an email to TPM. "They've voted with President Obama between 90 to 95 percent of the time in states where his approval rating is under 40 percent. In other words, it's pretty hard to get to the left of Mary Landrieu in Louisiana, Kay Hagan in North Carolina, Mark Begich in Alaska, Jeanne Shaheen in New Hampshire, or Mark Udall in Colorado and be at all viable. These Senators are already too extreme and liberal for their states, which is a big reason why all of their numbers are plummeting."