His supporters HAVE been speaking up. Conservative activists have been combating the likes of "Mother" Sheehan and others. Conservative talk show hosts have been fighting the good fight as well.
Now, GOP leaders who SHOULD be speaking up (like Frist), are wusses. However, the simple truth is, that they won't fight at all without strong leadership at the top. It sucks, but it is true. If they don't see their President waging war against his critics, they won't risk their necks to help. Politicians are survivial-oriented creatures and will run like hell from a President who lets himself look like a lame-duck under seige.
Sure, as long as it suited their agenda. The trashing of Bush during the Meir nomination was a good example where most "conservative" pundits stood.
For the politicians, because they are wimps, gives them no excuse. Most of the House and a few of the Senators owe their seats to GWB's coat tails.
If it wasn't for Rush Limbaugh, there would be no leadership at all on the Republican side except for the President.