WASHINGTON, Jan. 30 -- Kash Patel, President Donald Trump's pick to lead the FBI, will encounter deeply skeptical questioning from Democratic senators Thursday about his loyalty to the president and stated desire to overhaul the bureau as he faces a high-stakes hearing that will help determine his path toward confirmation.

Patel, a Trump loyalist who has railed against the FBI over its investigations into the president and claimed that Jan. 6 rioters were mistreated by the Justice Department, was picked in November to replace Christopher Wray, who led the nation's premier federal law enforcement agency for more than seven years.

A former aide to the House Intelligence Committee and an ex-federal prosecutor who served in Trump's first ad...