. Belt, 414 F.Sd 474, 478 (3d Cir2005), but exercise plenary review over the District Court's underlying legal conclusions. Freethought Soe'y of Greater Phila. v. Chester County, 334 F.3d 247, 955...36 (3d Cir.2003). A District Court's determina- tion whether a cooperation agreement has been breached is