Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE has a huge lead over Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE in Pennsylvania just three weeks before the primary there.

A Harper Polling survey released Tuesday found Clinton taking 55 percent over Sanders at 33 percent, with 12 percent undecided.

Clinton’s lead is down from the same survey in March, when she had a 30-point lead.

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There are 210 delegates up for grabs in Pennsylvania's April 26 primary. Sanders trails Clinton by about 300 delegates overall currently, and needs to start posting victories by wide margins if he’s going to catch her.

In the race to be the Democratic nominee to challenge incumbent Sen. Pat Toomey (R-Pa.), former Rep. Joe Sestak (D-Pa.) is in the lead with 41 percent support, following by former gubernatorial chief of staff Katie McGinty (D) at 31 percent.

McGinty has the support of the Democratic establishment, but continues to run behind Sestak in fundraising and in the polls.

Sestak narrowly lost to Toomey in 2010, a huge year for Republicans.

The Harper Polling survey of 603 likely Democratic voters in Pennsylvania was conducted between April 2-3 and has a 4-point margin of error.