Later, he enrolled in graduate school at the University of Minnesota, and continued his studies in History focusing on the working class and labor protest songs and poetry.

Human Geography followed in 1993, and Passion, Politics, Love being released in 1997 to acclaim, with Erik Hague from AllMusic calling it "top-notch, varied Americana".

[4][5] 2001 saw the release of Don't Want Your Millions, partly funded by the Illinois Arts Council, and considered a historic document of union and labor songs, featuring material from Studs Terkel, The Carter Family, Hazel Dickens and Lead Belly.

For years, Halker has been involved in the promotion and preservation of Woody Guthrie's musical legacy through concerts, lectures, writings, and media programs.

On volume 4 of the Folksongs of Illinois CD series Halker included Old Chy-Car-Go, a Guthrie song that was part of the performer's repertoire but had not been recorded before 2010.