(Bloomberg) -- The US regional banking system is at risk and the regulator’s failure to update and expand its insurance regime has “hammered more nails in the coffin,” Pershing Square’s Bill Ackman said. 

First Republic Bank was the second-biggest bank failure in US history, and the fourth regional lender to collapse since early March after Silvergate Capital Corp., SVB Financial Group’s Silicon Valley Bank and Signature Bank. JPMorgan Chase & Co. acquired First Republic on Monday, beating out rivals including PNC Financial Services Group Inc. 

The billionaire investor said First Republic wouldn’t have failed if the Federal Deposit Insurance Corp. temporarily guaranteed deposits while a new regime were created. “Instead, we watch the dominoes fall at great systemic and economic cost,” he said.

PacWest Bancorp, a Beverly Hills-based lender, plunged as much as 60% in postmarket trading Wednesday and has been considering a breakup or a capital raise, according to people familiar with the matter.

“Banking is a confidence game. At this rate, no regional bank can survive bad news or bad data as a stock price plunge inevitably follows, insured and uninsured deposits are withdrawn and ‘pursuing strategic alternatives’ means an FDIC shutdown over the coming weekend,” Ackman said.

Michael Barr, the vice chair for supervision for the Federal Reserve, and FDIC chair Martin Gruenberg are scheduled to testify at the Senate Banking Committee hearings on US bank failures later this month. 

The hearings come as Barr leads an effort at the Fed to review a range of rules that apply to firms with more than $100 billion in assets, including stress testing and liquidity requirements, following the failures. 

Ackman in March suggested that the FDIC should guarantee all of SVB’s deposits after its collapse, shortly before the US implemented emergency measures to backstop banks. He has repeatedly called for an improvement in the deposit guarantee program.

Ackman Warns of Accelerated Deposit Outflows After Fed Decision

He said then that he and Pershing Square had no direct exposure to SVB and that “collectively, my venture exposure is less than 10% of my assets.”

(Updates with comments on Ackman’s exposure and deposit guarantee advocacy in penultimate paragraph.)

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