K90 Controller described several 'false target' observations; noting the target was heading toward a Presidential TFR; adding this problem is pervasive and will lead to a wrong target determination at some point.

Narrative

RADAR ring around. POTUS movement and TFR in place over MVY. POTUS on the north east side of the island. Consistent with the same problem that has existed for well over a year; and has still not been fixed; a false target appeared on approximately the MVY 080R 5 DME and was tracking straight toward the restricted POTUS area. The target exists for 3 RADAR sweeps and then disappeared. The target appeared as a splat only at 3;000 FT. His flight path was directly at the location of the POTUS; which was between the splat and the airport. It took a minute to reconcile it; but with no primary target I made the determination that it was not a real target. However; if I had made the wrong determination? Ten minutes later; the exact same thing happened. The beacon code was 3671. At the time of both incidents; there were several witnesses in the room. The problem has become so rampant and so constant; that the RADAR at K90 has become a joke. No one cares; and I do not see K90 management doing anything to fix or mitigate the problem. It is only a matter of time before a wrong determination is made about these targets and disaster strikes. Recommendation; Fix the RADAR.