WASHINGTON—Timothy Geithner's role in calming the financial crisis landed him the coveted job of Treasury secretary last year. That same résumé is now dogging him.

In his next test, Mr. Geithner will find out this week how lawmakers are treating one of his main goals—revamping the nation's financial regulations—when Senate Banking Committee Chairman Chris Dodd unveils his new bill. In Washington, where perception can take on the status of fact, the political woes facing Mr. Geithner are diminishing his authority.

His...