WASHINGTON — Addressing a divided nation amid a determined GOP campaign to take his job, President Barack Obama is preparing to issue a populist cry for economic fairness as he aims to corral the sympathies of middle-class voters 10 months before Election Day.

Obama delivers his third State of the Union address Tuesday in a capital and country shot through with politics, with his re-election campaign well under way and his potential GOP opponents lobbing attacks against him daily as they scrap for the right to take him on.

Obama’s 8 p.m. CST address to a joint session of Congress and millions of television viewers will be as much as anything an argument for his re-election, the president’s biggest, best chance so far to offer a vision for a second term.

Senior political adviser David Plouffe said Tuesday morning the president is “happy to have a debate” about his performance.