WASHINGTON ― House Democrats will investigate whether President Donald Trump’s decision to delay security assistance to Ukraine was part of a pressure campaign to benefit him in the 2020 presidential election, potentially violating a host of legal and ethical rules.

Three House committees ― Foreign Affairs, Intelligence, and Oversight and Government Reform ― sent letters to the White House and State Department on Monday seeking documents about whether Trump and his personal lawyer, Rudy Giuliani, tried to get Ukraine to target a 2020 presidential candidate, former Vice President Joe Biden. The three panels announced the requests as part of a broad probe.

“The Trump Administration’s decision to withhold vital security assistance to Ukraine is only the latest in a series of actions in which President Trump appears to undermine U.S. foreign policy to placate Russia and place his personal interests above the national interest,” the Democratic chairmen of the committees said in a joint statement.

The letters came after The Washington Post’s editorial board wrote that it was “reliably told” the Trump administration suspended $250 million in U.S. military aid to get Ukrainian President Volodymyr Zelensky to relaunch a corruption probe into Biden and his son. Reportedly, a prosecutor previously investigated Biden’s son, who had worked for a Ukrainian energy firm.

The committee chairmen allege Trump focused on the investigation in a July 25 call with Zelensky, saying Ukraine’s corruption had inhibited its dealings with the United States. From there, Ambassador Kurt Volker, U.S. special representative for Ukraine, arranged a meeting between Zelensky and Giuliani. (The State Department reportedly called Giuliani “a private citizen” who “does not speak on behalf of the U.S. Government.”)

Key US lawmakers want to give Ukraine anti-ship and anti-aircraft missiles to counter Russia A new bill would also ask the president to determine whether Ukraine should be a major non-NATO ally, condemn Russia’s detention of 24 Ukrainian sailors and urge Russia to implement the Minsk II peace agreement.

The administration says the delay in sending military aid to Ukraine is mean to ensure it aligns with U.S. interests, but bipartisan pressure has been building for the Trump administration to end its review of the funds. In a letter last week, House Foreign Affairs Committee Chairman Eliot Engel, D-N.Y., and ranking member Michael McCaul, R-Texas, warned White House officials that the administration could contravene congressional appropriation of the funding.

Monday’s letter from Engel and the other chairmen warned that aid is vital to Ukraine’s defense against Russia and its proxies in illegally occupied Ukrainian territory.

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“If the President is trying to pressure Ukraine into choosing between defending itself from Russian aggression without U.S. assistance or leveraging its judicial system to serve the ends of the Trump campaign, this would represent a staggering abuse of power, a boon to Moscow, and a betrayal of the public trust,” the letter reads.