Three Democratic senators in a letter sent to the White House on Wednesday condemned President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE for calling on China to investigate former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE and his son.

Sens. Ed Markey Edward (Ed) John MarkeyA game theorist's advice to President Trump on filling the Supreme Court seat Watchdog confirms State Dept. canceled award for journalist who criticized Trump 3 reasons why Biden is misreading the politics of court packing MORE (D-Mass.), Tom Udall Thomas (Tom) Stewart UdallLWCF modernization: Restoring the promise OVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' Senate Democrats demand White House fire controversial head of public lands agency MORE (D-N.M.) and Jeff Merkley Jeffrey (Jeff) Alan MerkleyThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Sunday shows - Trump team defends coronavirus response Oregon senator says Trump's blame on 'forest management' for wildfires is 'just a big and devastating lie' MORE (D-Ore.) sent a letter to the president to "express our deep concern" about his request to China.

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"This invitation to a foreign government to interfere in the American electoral process not only violates your oath of office, but also undermines the very values for which this country stands," the letter reads.

The letter comes after Trump had told reporters earlier this month, “I would think that if they were honest about it they’d start a major investigation into the Bidens.”

The senators said Trump should instead be looking to protect the "sanctity" of the election process.

"We believe that — consistent with your oath of office — the President of the United States must protect and defend the Constitution of the United States," the senators wrote. "At a minimum that includes ensuring the sanctity of our electoral process and not inviting foreign interference into it."

Trump's request to China comes as the House has launched an impeachment inquiry over his request Ukraine look into Biden, a front-runner for the Democratic presidential nomination.