Rep. Tim Holden (D-PA) became the latest member of the fiscally conservative Blue Dog Coalition to fall Tuesday after failing to win his district's Democratic primary.

Holden’s loss could be a harbinger for other Blue Dogs seeking reelection this year amid redistricting and a difficult political environment for moderate lawmakers. Holden also becomes the second incumbent House member to lose to a primary challenger. Rep. Jean Schmidt (R-OH) lost her primary last month.

Attorney Matt Cartwright defeated Holden. Cartwright raised $300,000 more than Holden during the first quarter and poured in $390,000 of his own money into the primary. He also benefited from the anti-incumbent super PAC Campaign for Primary Accountability’s $200,000 ad campaign against Holden.

It was an uphill battle for Holden from the start as he faced a district that was 80 percent new territory. The Republican-controlled Pennsylvania state legislature redrew Holden’s district to include more Democratic-leaning areas – and fewer voters familiar with his 19-year House tenure. In contrast, Cartwright had more name recognition due to a local TV presence and close ties to the northeastern Pennsylvania area’s Democrats.

Holden bucked his party on several major issues, including cap-and-trade legislation and the 2010 health care reform bill Cartwright unseated the incumbent largely in part by framing his voting record as too conservative for a district with a high concentration of Democrats..

The 2010 midterm elections washed out the ranks of many centrist members of Congress, including several Blue Dogs. Twenty-four members remain, but five intend not to seek reelection. Still others, like Holden, face shaky electoral prospects.