WASHINGTON — In his first 21 months on the job, Randal K. Quarles, the Federal Reserve’s vice chairman for supervision and regulation, met at least 22 times with partners at his former law firm, Davis Polk & Wardwell, which represents many of the nation’s largest banks.

Those meetings, disclosed in public schedules and other releases, suggest a closeness between America’s most important bank regulator and the industry he watches over. Mr. Quarles was a bank lawyer at Davis Polk in the 1980s and ’90s. At the Fed, he has conferred with former colleagues there, including Randall Guynn, a close friend . They at least occasionally came alongside officials of banks they represent, including Goldman Sachs, and trade groups including the Securities Industry and Financial Markets Association.

But the gatherings also suggest Mr. Quarles is meticulously completing the job President Trump nominated him to do. He is perhaps the most central player as regulators reassess bank rules put into place quickly, and often bluntly, in response to the 2008 financial crisis. Lawyers at Davis Polk, which has built a reputation as a top financial services practice, know how the rules are working and what the banks find problematic.

That tension underlines a key challenge of financial regulation in 2019. Most current and former regulators agree that post-crisis rules could be improved . Banks’ input can help policymakers determine which adjustments will enable more lending without encouraging excessive risk-taking. But catering to their interests too intently risks reigniting vulnerabilities in a financial system with a record of sinking the entire United States economy.