In Trumpworld, "much" can mean "anything more than 0.01%".
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So far the Administration has been primarily engaged in renewing or upgrading existing "wall" and hasn't added a whole lot of new "wall", so it really depends on how you classify "new" wall versus renovating "wall" (i.e. if you consider replacing older, shorter wall with new higher wall as "adding" wall), but from looking at the sections that have been worked on (or are currently under construction) principally in the Juarez, Mexicali and Tijuana areas, it looks to be more like 10% (a rough guestimate) of the 700 or so miles of the existing "wall".