Indeed. He's not getting paid (in both actual dollars and in attention) for having walls built. Whether the wall gets built or not is entirely irrelevant as long as he gets votes.

Unfortunately, selling "walls" (policy) is his actual job.

He's like a vacuum cleaner salesman who can always get his foot in the door, but can never manage to sell a unit.

Not quite.

He's like a vacuum salesman who promises to give his customers dishwashers and toasters for free if they buy a vacuum cleaner.

When they buy the vacuum cleaner, it turns out he lied about the other goods but they still ended up with the vacuum cleaner. But what a lot of people really wanted was the dishwasher.

I may have pushed the analogy a little too far...