This phase Ib trial studies the side effects of MDM2 inhibitor AMG-232 and radiation therapy in treating patients with soft tissue sarcoma. MDM2 inhibitor AMG-232 may stop the growth of cancer cells by blocking some of the enzymes needed for cell growth. Giving MDM2 inhibitor AMG-232 and radiation therapy before surgery may make the tumor smaller and reduce the amount of normal tissue that needs to be removed.