Rove, Bush et al simply do not realize the peril they're in. If this Act passes, Bush is impeached; simple as that. There will be those who worked precints in '04 that will be out in force supporting the Dem House managers. If the Senate flips as well, this could go all the way.
While signing the Senate abomination should IMHO constitute an impeachable offense, the only way Bush would be able to sign it would be if a majority of House members vote for it. Since I can't see how any reasonable congresscritter could impeach a president for signing legislation that congresscritter voted for, I don't see how Bush could be impeached for that unless you're suggesting that Democrats would vote for this legislation but then vote to impeach Bush out of spite.