Some U.S. House races of interest in Pennsylvania:

—In the heavily Democratic 13th District, which include parts of Philadelphia, four Democrats are seeking the congressional seat being vacated by Democratic Rep. Allyson Schwartz, who is running for governor.

Former Rep. Marjorie Margolies, who previously held the seat from 1993-1995, trails the other candidates in campaign cash, but is getting a boost from former President Bill Clinton, who will headline a steakhouse fundraiser on her behalf at the tony Warwick Hotel in Philadelphia. Margolies is Chelsea Clinton's mother-in-law.

She is competing against a political newcomer, physician Val Arkoosh, who raised more than $900,000 last year; state Rep. Brendan Boyle, who has the support of several labor unions; and state Sen. Daylin Leach, a progressive who has the endorsement of the Howard Dean-aligned Democracy for America and MoveOn.org.

Margolies has received criticism from her Democratic opponents for skipping out on several candidate forums; she is expected to attend one on Monday.

The winner of the Democratic primary will face either of the two Republicans competing in their primary, Carson Dee Adcock and Beverly Plosa-Bowser.

—In the rural heartland of the 9th District, GOP Rep. Bill Shuster faces a tea party-affiliated challenge from retired Coast Guard Capt. Art Halvorson. Farmer Travis Schooley also is running.

In the state's most conservative district, Shuster, who chairs the powerful House Transportation and Infrastructure Committee, has drawn criticism from his opponents who see him as representing big government and spending in Washington.

Still, with more than $1.3 million on hand, Shuster dwarfs his opponents in campaign spending power and already has launched ads touting his opposition to the federal health care law.

Democrat Alanna Hartzok, a mental health professional, is running unopposed in her primary.