As Amy Walter points out here, there are a number of new members in very competitive districts who pledged – in varying degrees – not to support Pelosi. There are good reasons to believe that provided a margin of victory, though obviously there’s no real way to know. Very, very few of them have signed this letter. The vast majority of the signers are from very safe districts. So the upshot here is that this likely forces freshmen Dems who will have very hard reelection races in two years to start their term with a tough vote which could get them tossed in two years.