The Dow Jones Industrial Average plunged more than 400 points Monday morning, following a weekend attempt by Treasury Secretary Steven Mnuchin Steven Terner MnuchinHillicon Valley: DOJ proposes tech liability shield reform to Congress | Treasury sanctions individuals, groups tied to Russian malign influence activities | House Republican introduces bill to set standards for self-driving cars Treasury: Trump's payroll tax deferral won't hurt Social Security Treasury sanctions individuals, groups tied to Russian malign influence activities MORE to calm the markets.

Mnuchin said Sunday that he spoke with the heads of six major banks — Bank of America, Citi, Goldman Sachs, JP Morgan Chase, Morgan Stanley and Wells Fargo — and reported that they had "ample liquidity."

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He also said he would convene a call with the president's working group on financial markets and a group of key regulators.

But the unusual message may have backfired, with analysts noting that the group Mnuchin was calling together was the same as the "Plunge Protection Team" that met at the height of the 2009 financial crisis.

Markets have also been spooked by reports that President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE is looking to fire Federal Reserve Chairman Jerome Powell. The move would be seen as undermining the Fed's institutional independence, which is a key element in the country's financial system.

U.S. stock markets early Monday continued a decline that last week saw the Dow's worst trading week in a decade. Traders will have a shortened day on Christmas Eve and markets will be closed on Tuesday for the Christmas holiday.