Some top Republican lawmakers on Monday assailed the Trump administration's move to open a criminal investigation into Jerome H. Powell, the Federal Reserve chair, and warned that the central bank's independence and credibility was at risk. The backlash could potentially constrain President Trump's efforts to exert legal pressure on Mr. Powell, whose term as chair expires in May but who can remain on the Fed's policy-setting board of governors until 2028. The Justice Department served the central bank with grand jury subpoenas late on Friday and is investigating whether Mr. Powell lied to Congress last year when testifying about the renovation of the Fed's headquarters.