David Brock is a political activist and author for what political party?
Media Matters for America:  Set up as a tax-exempt, nonprofit organization, MMfA was founded in 2004 by journalist and political activist David Brock as a counterweight to the conservative Media Research Center. David Brock:  He has been described by "Time" as "one of the most influential operatives in the Democratic Party".
He has been described by "Time" as "one of the most influential operatives in the Democratic Party".