The letters, dated October 24, went to the leadership of JPMorgan Chase, Bank of America, Citigroup, Wells Fargo, Goldman Sachs and Morgan Stanley, according to Bloomberg, Axios and The Insider. Similar requests were sent to the port authorities of Houston, Beaumont and Corpus Christi in Texas, and of New York and New Jersey.

They were signed by Senators Chris Coons, Elizabeth Warren and Ron Wyden, and by Representative Gregory Meeks. All four hold influential positions on committees dealing with foreign relations, banking and finance, and some could chair those committees if Democrats win the November 3 elections and take a majority in Congress.

In the letters, the lawmakers urge the banks and ports not to assist the "purchase, transportation, import, unloading, storage, financing or distribution" of Russian diesel on US territory, and not to take part in supplies to other markets. According to the authors, the deal "raises serious national security concerns, since it will finance Russia's brutal and illegal war against Ukraine."

The Democrats also warned that Russian diesel supplies to the US raise serious legal questions and could become the subject of litigation and congressional investigations.

Trump announced on October 9 that he had agreed with Putin on supplies of Russian diesel to world markets. To that end, the US Treasury temporarily eased sanctions on Russian diesel until April 7, 2027. According to Trump, Russia is to supply more than 300,000 tonnes of diesel immediately, another 500,000 tonnes in November, and then an additional million tonnes.

According to Reuters, the first tanker with Russian diesel — the Malta-flagged Agioi Fanendes — left the Baltic port of Primorsk on October 22 with 40,000 tonnes of cargo. It is expected to arrive at its destination on November 7, after the results of the midterm congressional elections become known.

Trump explained the arrangement with Putin as an effort to lower US diesel prices, which rose sharply because of the war with Iran that he started. The Moscow Times cites CME Group data: before Trump's announcement, the November diesel futures contract cost $4.88 a gallon; it now costs $4.99, and the December contract $4.8. The retail price of diesel both before and after has exceeded $6 a gallon.

The White House criticized the Democrats' initiative. Administration press secretary Taylor Rogers said the opposition "once again demonstrates the absence of any program to improve the lives of Americans" and intends to continue its "decade-long obsession with investigations of President Trump."

Republican Mitch McConnell, chairman of the Senate Appropriations Subcommittee on Defense, criticized Trump in a column for The Wall Street Journal. He called attempts to reach agreement with Putin "strategically naive and morally bankrupt" and said that "servile accommodation toward Russia that rewards an aggressor with sanctions relief will not convince Putin to stop." Dmitry Peskov, commenting on the start of supplies, said the first tanker "has gone to its addressees, to its buyers, and they will continue rhythmically," without specifying the destination country.