The Jefferson Memorial is a "nonpublic forum reserved for the tranquil commemoration of Mr. Jefferson's legacy" (4).

The Park Service regulations that require a permit for demonstrations (including "forms of conduct which involve the communication or expression of views or grievances, engaged in by one or more persons, the conduct of which has the effect, intent or propensity to draw a crowd of onlookers") were properly interpreted as applicable to dancing, as a "conspicuous expressive act with a propensity to draw onlookers" (7).

Even though permits are generally only required for groups of 25 or more people, smaller groups (including groups of one person) must still meet the conditions required for issuance of a permit if they wish to engage in a demonstration.

One of those "other conditions" is that no permits are issued for inside the Jefferson Memorial; i.e. a condition of issuance is that the demonstration be outside the Memorial.

It would be a different story if the Memorial were a public forum, or a public area that has long "been devoted to assembly or debate" or a limited public forum, which is public property expressly "opened for use by the public as a place for expressive activity" (8-9). But the Memorial is a nonpublic forum, which the government "may reserve... for its intended purposes... as long as the regulation on speech is reasonable and not an effort to suppress expression merely because public officials oppose the speaker's view" (9).

Just because the Memorial is open to the public doesn't mean it's a public forum: it's open to the public with a purpose other than that it serve as a space for expression.