WASHINGTON (AP) ― Barack Obama vows to put up a fight Tuesday in his second debate with Republican challenger Mitt Romney, a promise the president will need to keep if he is to overcome his lackluster, momentum-stalling performance in the candidates’ first debate two weeks ago.

Romney will likewise need to turn in a repeat of his strong showing in the initial face-to-face-competition, a performance which propelled him into a virtual tie in nationwide polling. Obama still hangs on to small leads in many of the nine key swing states that likely will determine which man occupies the White House on Inauguration Day, Jan. 20.

The so-called battleground states ― those that do not reliably vote either Republican or Democratic ― take on outsized importance in the U.S. system where the president is chosen not by the nationwide popular vote but in state-by-state contests.

The Tuesday debate at Hofstra University in Hempstead, New York, falls exactly three weeks before Election Day in what promises to be one of the closest presidential contests in recent U.S. history. The Nov. 6 vote takes place against a backdrop of deep partisan divisions among Americans and near political deadlock in Congress.

The president’s first act in this critical campaign week was to announce a new battleground state advertisement featuring voters discussing the ways their economic conditions have improved during his term. The ad was hitting the airwaves as Obama and Romney remained closeted with advisers in debate preparation.

The ad signaled Obama’s intention to try to turn the tables on Romney by focusing in part on the economy during Tuesday’s town hall-style meeting in which independent voters will pose questions to the candidates. The economy is the No. 1 issue for voters in this election, and one the Romney camp has long considered a weak point for the incumbent.