If you can’t stomach the debate this evening, but are still in the mood for some TV viewing in a political vein, catch Robert Altman’s “Tanner on Tanner.” The first of the four-part series airs tonight at 9 p.m. on the Sundance Channel. A follow up to Altman’s well received 1988 TV series about faux presidential candidate Jack Tanner (“Tanner ’88”), “Tanner on Tanner” puts the focus on his daughter, Alex Tanner, played by Cynthia…