Here's a partial answer....
http://www.washingtonpost.com/wp-dyn/content/article/2006/04/11/AR2006041101643.html
Apparently, the Republicans offered an amendment to reduce the felony to a misdemeanor, and all but 8 Democrats voted against it. They're now claiming that was okay, because they 'weren't helping the bill get passed.'
Republicans proposed HR 4437, an amendment to our current Immigration and Naturazition Act. HR 4437 will make illegal presence in the US a criminal offense, and in the original version, illegal presense is also a felony.
After the White House protested, Sensenbrenner offered an amendment to make illegal presense a misdemeanor instead of a felony.
Democrats believing that Republicans had overreached joined 65 law-and-order Republicans to oppose the Sensenbrenner amendment.
The original language stayed, and the overwhelming Republican caucus voted for the whole bill.
The "illegal presense is a felony" was introduced by Republicans.
Now trying to blame the Democrats is lame. After all, the Democrats want the status quo, which is a civil violation (fine), not jail time. And most illegal aliens don't even know the difference between a felony or a misdemeanor. All they know is that the Republicans want to make them criminals, instead of civil offenders.