Deutsche Bank became the latest large company to cut ties with Donald Trump, with the firm that has propped up the Trump Organization for two decades reportedly announcing it would no longer do business with the disgraced president.

The German bank’s move – reported by the New York Times – follows Wednesday’s deadly attack on the US Capitol building by a mob of Trump supporters. The number of corporations disassociating themselves from Trump is now turning into an avalanche.

Deutsche Bank has been Trump’s most important lender. The Trump Organization, fronted by his two older sons, owes the bank about $340m in outstanding loans. After a series of bankruptcies in the 1990s, it was the only bank willing to give Trump money.

The relationship has survived various scandals. In 2008, Trump sued the bank’s real estate division after he defaulted on a $40m repayment, used to fund the construction of the Trump International Hotel and Tower in Chicago. He accused Deutsche of co-causing the financial crisis and demanded $3bn in compensation.

Instead of dumping him as a client, Deutsche’s private wealth division stepped in and loaned him more money to pay off the existing debt. Deutsche has resisted efforts by Democrats in the House and Senate to explain its relationship with Trump – and to clarify if Russian state banks or entities underwrote some of his debts.

But the bloody events of last week and the looming threat of a second impeachment trial appear to have finally persuaded Deutsche’s managers to terminate its association with Trump. A Deutsche spokesperson refused to elaborate on Tuesday, telling the Guardian: “We decline to comment.”

It is unclear if the decision extends to other members of the Trump family. The president’s daughter Ivanka Trump and son-in-law Jared Kushner are both Deutsche clients.

In the last few days Twitter and Facebook have removed Trump from their platforms, with Trump’s Twitter account permanently suspended. Leading firms including Coca-Cola, the Marriott hotel chain, AT&T, Walmart and General Motors have said they will suspend political donations.

The firms have said they will no longer give money to Republican representatives who have promoted Trump’s false claim that November’s election was rigged, and that Trump “won”. In the past they have donated to candidates from both parties.

Several of the biggest banks in the US have said they too will suspend donations from their political action committees. They include JPMorgan Chase, Goldman Sachs, Citigroup and Morgan Stanley. According to Reuters, Deutsche had been looking to end its links with Trump since November, having grown tired of negative publicity.

“We are proud of our constitution and stand by those who seek to uphold it to ensure that the will of the people is upheld and a peaceful transition of power takes place,” Christina Riley, the head of Deutsche’s US operations, wrote last week on LinkedIn.

Another of Trump’s key lenders, Signature Bank, said it was closing his two personal accounts, which held a combined $5.3m in deposits. The New York bank has previously financed Trump’s Florida golf course. Ivanka Trump sat on its board.

The bank called on Trump to quit. “We witnessed the President of the United States encouraging the rioters and refraining from calling in the National Guard to protect the Congress in its performance of duty,” it said in a statement.

“At this point in time, to ensure the peaceful transition of power, we believe the appropriate action would be the resignation of the President of the United States, which is in the best interests of our nation and the American people”.

On Sunday, the US Professional Golfers’ Association said it would no longer hold its championship in May 2022 at Trump’s New Jersey golf club. Its decision to scrap its deal with the Trump Organization reportedly left Trump “gutted”.

“It has become clear that conducting the PGA championship at Trump Bedminster would be detrimental to the PGA of America brand, and would put at risk the PGA’s ability to deliver our many programmes, and sustain the longevity of our mission,” Jim Richerson, its president, said in a video statement.

The Trump Organization responded on Sunday, saying: “We have had a beautiful partnership with the PGA of America and are incredibly disappointed with their decision. This is a breach of a binding contract, and they have no right to terminate the agreement.”

The decision not to use Trump’s resort to host the second of four major tournaments on the tour’s calendar was a heavy loss to a president who has emphasised his portfolio of golf resorts and spent time – too much, his critics say – on the course while in office.