Santos faces a federal trial next year.

Following his expulsion from the House of Representatives on Friday, George Santos faces an even tougher and more uncertain challenge in a federal court on Long Island.

Mr. Santos has been charged with 23 felonies for his role in a series of schemes involving his personal and campaign finances. He has pleaded not guilty on all counts.

Prosecutors in the Eastern District of New York say he falsified campaign filings, artificially boosting his campaign’s financial position with bogus donations from family members and fictitious loans.

They have also accused him of stealing from donors by repeatedly taking money from their credit cards without permission and distributing the money to his and others’ campaigns, as well as to his own bank account.

In addition, Mr. Santos faces charges related to his use of an unregistered super PAC called RedStone Strategies. Prosecutors say Mr. Santos and an associate solicited $50,000 in contributions from RedStone with the promise that they would be used in ads supporting Mr. Santos’ campaign.

Instead, prosecutors say, Mr. Santos used the money for personal expenses, including designer goods and credit card payments. (House ethics investigators said Mr. Santos’ use of RedStone as a personal piggy bank was more widespread and accused him of pocketing more than $200,000.)

Prosecutors have also accused Mr. Santos of collecting more than $20,000 in unemployment benefits while he was actually employed.

Mr. Santos has vociferously defended himself, saying that most of the charges against him are either misunderstandings or the result of negligence by his treasurer, Nancy Marks, who he says was “rogue.” Ms Marks pleaded guilty to one conspiracy charge earlier this year.

Mr Santos has also claimed he had no involvement in his campaign finances. But a damning report from the House Ethics Committee has complicated Mr. Santos’ defense and provided evidence that he reviewed weekly financial reports and approved invoices.

In September, prosecutors said they were discussing “possible further steps” with Mr. Santos’ team, leading to speculation that the congressman could negotiate a plea deal that could include his resignation. But Mr. Santos repeatedly said he had no intention of resigning.