Subject: Re: Harris and the Dem tax proposals,
IF Buffett donates untaxed wealth why not make the Foundation pay the 20 % cap gain rate from the proceeds when they sell? Simple and easy, no?

The Foundation is (I assume) a charitable entity that's exempt from paying taxes altogether. They don't have to pay anything when they sell.

You could change that, of course (theoretically almost any aspect of the tax code can be amended). But it's probably much more complicated to carve out that one specific instance of tax exemption for charitable entities, rather than to require a tax payment by the donor at the time of transfer as a way of blocking that 'escape hatch' from the appreciated asset income tax.