The Democratic challenger in a special congressional race in Pennsylvania has taken a big fundraising lead over his Republican opponent in a traditionally Republican-leaning district.

Federal Election Commission filings on Thursday show Democrat Conor Lamb has raised more than $3.3 million in the first seven weeks of 2018, according to The Associated Press, nearly five times as much as state Rep. Rick Saccone (R).

The latest numbers show Lamb with a runaway lead in fundraising, though the 33-year-old prosecutor lags behind Saccone by single-digit margins in most polls going into the last three weeks before the special election to fill the seat left vacant by Rep. Tim Murphy Tim MurphyBiden receives endorsements from three swing-district Democrats A federal abortion law might be needed Female Dems see double standard in Klobuchar accusations MORE's (R) resignation in October.

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Lamb, who has poured money into radio and TV ads in the Pittsburgh area, has far outspent Saccone and still has $837,000 in cash on hand, compared to his opponent's $303,000.

The close race, in a district where President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE won by nearly 20 points in 2016, has spurred GOP groups to spend nearly $5 million to bolster Saccone, while returning fire with attack ads toward Lamb.

But Democrats have given only tepid support for Lamb despite the possibility of a red district upset in a year the party aims to regain control of the House, requiring them to flip 24 congressional seats.

The Democratic Congressional Campaign Committee spent $300,000 on Lamb's campaign at the outset of the race but said it will not pour any more money into the close race. A spokesman for the committee said Lamb has enough resources and momentum to take down the veteran state legislator.

Trump will appear in Pennsylvania for a campaign rally later this month just outside of Pittsburgh.

Vice President Pence appeared at a fundraising event for Saccone last month in an effort to bolster his campaign.