Democrats Score Sought-After Senate Candidate in Pennsylvania

But Katie McGinty's entrance into the Senate race ensures a heated, divisive primary for the right to challenge Sen. Pat Toomey.

Pennsylvania Democrat Katie McGinty will resign her position as chief of staff to Gov. Tom Wolf on Thursday in preparation to run for the United States Senate, two sources with direct knowledge of the situation tell National Journal.

McGinty will not make a formal declaration Thursday that she's running for the seat held by Republican Sen. Pat Toomey, according to the sources. But her decision to resign her high-profile job after only seven months all but guarantees a Senate campaign, sources added. They expect a formal campaign announcement within weeks.

McGinty's entrance would be a major victory for Democrats in Washington, who have scoured Pennsylvania looking for a top-tier candidate in what should be a politically-crucial Senate battleground in 2016. Party leaders are wary about the only Democrat in the race, former Rep. Joe Sestak, concerned that his unwillingness to listen to strategic advice could cost them a winnable race against the well-entrenched Toomey.

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But Sestak is certain to stick in the race against McGinty, setting up a highly competitive primary battle. In the 2010 campaign, he ignored pressure from Democratic leaders—including President Obama—to stop his primary run against party-switching Sen. Arlen Specter. Sestak surprised political pundits by winning that race, before losing narrowly in the general election to Toomey. Sestak has argued that his close race against Toomey in a year when Republicans won overwhelmingly across the country—and in Pennsylvania—is a sign of his political strength.

McGinty has a limited electoral profile. She ran for governor in last year's Democratic primary and finished last among four contenders for the nomination. She's never held elective office before, and starts at a significant fundraising disadvantage against Sestak, who by April had already banked $1.7 million for his campaign. Sestak has been campaigning across the state for nearly a year, even walking over 400 miles after announcing his candidacy to draw publicity for the campaign.

But McGinty, a former top environment adviser both to former Vice President Al Gore and former Pennsylvania Gov. Ed Rendell, has long been considered a rising star in the Democratic Party and is popular among party leaders and activists alike. Unlike Specter, she's not a former Republican with a record that would provide Sestak plenty of damaging material in a Democratic primary. And the opportunity for her to run on the top of the ticket with Hillary Clinton is an appealing notion for Democrats, who could campaign on electing the first female president and first female senator from Pennsylvania. EMILY's List, the Democratic women's group, has been privately enthusiastic about her rumored candidacy for a while.

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If Democrats can win the Pennsylvania Senate race, their path to winning back the majority becomes much easier. They're optimistic about their chances against Sen. Mark Kirk in Illinois and Sen. Ron Johnson in Wisconsin, both Republicans running in Democratic-friendly states. If they were to win in Pennsylvania, they could win back the majority by winning only one more GOP-held seat (or two, if a Republican won the presidency).

The Democratic Senatorial Campaign Committee is not expected to initially endorse either candidate, a source inside the group said, but officials there won't rule out getting behind either Sestak or McGinty before the primary.