House Minority Leader Nancy Pelosi Nancy PelosiHoyer: House should vote on COVID-19 aid — with or without a bipartisan deal Ruth Bader Ginsburg lies in repose at Supreme Court McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE (D-Calif.) warned Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.) in a letter on Thursday that Republicans must not end the chamber's probe into Russia's election interference, saying national security is at stake.

"The American people deserve a comprehensive and fair investigation into Russia's attack. Political haste must not cut short valid investigatory threads. Key questions about foreign interference in our elections remain, and must be thoroughly investigated," Pelosi wrote.

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"Nothing less than America's democracy and national security are at stake, and therefore we must fully investigate Russia's assault on our election systems to prevent future foreign attacks," she continued.

The House Intelligence Committee has been investigating Russia's election interference all year, but media reports have suggested Republicans on the panel are pushing to close out the investigation soon despite protests from Democrats who say key witnesses have yet to be interviewed.

Responding to Pelosi's letter, Ryan spokeswoman AshLee Strong said the investigation would conclude "when the Committee has reached a conclusion."

“To suit her political agenda, Leader Pelosi would like to see this investigation go on forever. That is obvious. Whether it concludes next month, next year, or in three years, she will say it is too soon. For nearly a year, this Committee has been following the facts, and it continues to do so," Strong said in a statement.

"The investigation will conclude when the Committee has reached a conclusion. It is also the Committee’s responsibility to provide recommendations to Congress to ensure what took place last election never happens again. One would hope that Leader Pelosi would want those recommendations in time to implement them before the election coming just next year."

Rep. Adam Schiff Adam Bennett SchiffPelosi, Democrats unveil bills to rein in alleged White House abuses of power Chris Matthews ripped for complimenting Trump's 'true presidential behavior' on Ginsburg Trump casts doubt on Ginsburg statement, wonders if it was written by Schiff, Pelosi or Schumer MORE (Calif.), the ranking Democrat on the Intelligence panel, has warned that the investigation is at risk. He tore into the committee's chairman, Rep. Devin Nunes Devin Gerald NunesOvernight Defense: Stopgap spending measure awaits Senate vote | Trump nominates former Nunes aide for intelligence community watchdog | Trump extends ban on racial discrimination training to contractors, military Trump nominates former Nunes aide to serve as intel community inspector general Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election MORE (R-Calif.), on Thursday, accusing him of "doing the work of the White House."

"It's more of the same problem we saw early in the investigation when the chairman had difficulty removing himself from his role during the campaign of being a proxy for the White House," he said.

The Senate Intelligence Committee is conducting its own investigation into Russia's election activities, as is special counsel Robert Mueller at the Justice Department.