Edward Davis was always the obvious choice for Mayor Tom Menino’s next police commissioner. He comes from outside the polarized internal politics of the Boston Police Department (BPD), but is familiar to Menino for the mayor’s comfort level. The only real question was whether Davis was willing to leave his position as chief of police in Lowell to do it. He was.

Now comes the hard part.

While it’s true that Boston is a whole new league for him — five of Boston’s 12 policing districts had more robberies than all of Lowell last year — it’s a challenge that Davis appears eminently qualified to handle.

But his success may depend on Bostonians who, let’s face it, do not always make it easy to succeed in this town.

Here are five keys to whether Ed Davis becomes a hero in the department and the city, or just staggers along until he, like his predecessors, heads for more pleasant pastures.

Give-and-take from the unions. The BPD unions often make reform and improvement nearly impossible. Davis, who has had problems with the unions in Lowell, will almost certainly want to make changes (perhaps a serious reduction in paid details or a reorganization of shift assignments?) that require union sign-off. Davis should be ready to offer something in exchange for the concessions he wants — and the unions need to accept it.

Authority from the mayor. Menino can’t help watching — and often directing — every move his commissioners make. (Davis’s immediate decision to name Al Goslin as his second-in-command, while a smart move, has Menino’s fingerprints all over it.) Menino not only has to give Davis a long leash, he needs to continually signal his disengagement in the decision-making process so that everyone knows who’s boss at the BPD.

Cooperation from community leaders. This means actually doing what Davis asks them to do, not bitching that Davis doesn’t listen to their advice. Kathleen O’Toole did community outreach until she was blue in the face, but constantly found herself lectured to rather than listened to. Davis’s belief in high-visibility policing in crime-ridden neighborhoods, for example, will inevitably raise fears of increased harassment of minorities. Bostonians may need to bite their tongues and follow Davis’s lead, at least for a while.

Resources from funders. Davis holds a broad view of prevention, intervention, and enforcement, and that requires more than cops and guns. Perhaps a Deval Patrick administration would help restore substance-abuse treatment, school and after-school funding, and job programs, among other things. Local private foundations, which have not filled the gaps, should ask Davis how they can help out. The city should keep pushing money toward bigger academy classes in order to rebuild the size of the force, says council president Michael Flaherty.

Patience from everybody. “Just as the crime situation didn’t happen overnight, it won’t go away overnight,” says Suffolk County Sheriff Andrea Cabral. “You have to give this person the time to work.” Likewise, Davis will need time to find the right people for the right jobs and change the culture where necessary. “In Boston, people like to pile on before the whistle even blows to start the play,” says Ralph Martin, former Suffolk County district attorney. “People need to give him a chance.”

Of course, if Davis hasn’t delivered some results by the end of next summer, let the piling on begin.