Testing the limits of presidential power, Donald Trump this week tightened his grip on U.S. government agencies that for years have taken pride in their independence overseeing such matters as elections,

The executive order would affect agencies like the SEC and FDIC, but it excludes the Federal Reserve's Board of Governors and Open Market Committee.

A regulatory expert said the directive will likely be challenged in court, as Congress has largely shielded some of the affected agencies from involvement by the White House.