The verb "did": dummy or lexical one?

In these states, the AP can use results from https://www.ap.org/content/politics/elections/ap-votecast/about, a survey of the American electorate aimed at determining why voters voted how they did, to confirm a candidate's victory.

From the Associated Press.

In the sentence above, is the verb "did" a lexical one or a dummy (the way the "do" works in questions and negations)?