For a fleeting moment this month, investment bankers in leveraged finance — the lucrative lending that oils the wheels of M&A and feeds the $1.3 trillion market for collateralized loan obligations — had rare cause for cheer.

Wall Street’s vaunted leveraged finance desks are reeling. Billions of dollars in losses on mistimed loans have forced them to dramatically scale back lending, leaving the private equity firms that rely on them to help fund acquisitions in a bind.

One of the most lucrative money-making machines in the world of finance is all clogged up, threatening a year of pain for Wall Street banks and private-equity barons as a decade-long deal boom goes bust.

They are creations of easy credit, beneficiaries of central bank largesse. And now that the era of unconventional monetary policy is over, they’re facing a challenge like never before.

They were once America’s corporate titans. Beloved household names. Case studies in success.

The biggest private equity firms in the U.S. are unleashing a flurry of new leveraged buyouts and debt-funded dividends, seeking to make up for lost time after staying on the sidelines for much of 2020.