From the National Mall & Memorial Parks Superintendent's Compendium
Section 2.15 Pets
Pusuant to 36 CFR 2.15 (a)(2),(5), pets are prohibited inside the Washington Monument, the Jefferson, Lincoln and World War II Memorials, Ford’s Theatre and the Petersen House, except for guide dogs for visually or hearing-impaired persons. Pets on a leash are allowed in the Franklin Delano Roosevelt Memorial.
Pets must be physically restrained at all times either by crating, caging or on a leash no more than six (6) feet in length and waste must be disposed of by placing in a plastic bag and depositing in a trash receptacle.