WASHINGTON (Reuters) - President Bush set up a showdown with Senate Democrats on Monday by renominating 20 failed judicial nominees, many of whom had been denounced by critics as "right-wing extremists." The renewed battle over the nominees promises to produce plenty of fireworks as Bush begins his second term with an expanded Senate Republican majority and still-defiant Senate Democrats. Senate Majority Leader Bill Frist, a Tennessee Republican, has threatened to change the Senate's rules to prevent any more procedural hurdles known as filibusters against judicial nominees. Senate Minority Leader Harry Reid of Nevada has vowed Democrats are "not going to...