Just to mix things up, let's post a broken campaign promise from Obama. The promise was to end no-bid government contracts worth more $25,000.
PolitiFact | End no-bid contracts above $25,000 - Obama promise No. 30:
The promise was apparently completely unrealistic since in some cases government contracts are urgently needed, and the bidding process is too long. The Heritage Foundation official from the link gives the example of soldiers in Iraq who need sleeping bags ASAP. It would only make sense to get that done without going through the bidding process.
The same logic applies to political promises to end spending earmarks. Sometimes earmarks make sense when there's an emergency. Example: Louisiana Congressmen using earmarks to get funds to their state in response to Hurricane Katrina.
Obama is a politician, so of course he is going to break campaign promises, that is what politicians are born for, to break promises. It is also a given that he will disappoint his supporters, every president does that.
The question is how many promises does he break, and how many he keeps. If he keeps a majority of them, people will forgive him for not keeping the rest.
As to earmarks, Obama doesn't have the authority to get rid of them, that is the job of the Congress. Obama can speak out agaisnt them, and he has done so on several occasions.