One of the weird things about the legislative process is that a congressman can propose an amendment, and vote for it, but then not have to vote for the actual bill to which the amendment is attached. It’s bizarre. Apparently the same principle does not apply to earmarks:
Top members of the Appropriations Committee might, for instance, grant a lawmaker’s request for a few million dollars for an important project back home. That lawmaker would then be obligated to support the entire multibillion-dollar bill despite possible reservations. Woe to the person who gets an earmark and then opposes the bill; chances for a future earmark would be somewhere between zero and none.
Note that there doesn’t seem to be any formal law here, just a cultural norm. With earmarks on the way out, one wonders how — if at all — the amendment process will change.