Senator Barack Obama has chosen to spend Tuesday night not in Kentucky or Oregon, the two states that will be holding their primaries that day, or even at his home in Chicago. Instead, Mr. Obama’s staff announced on Saturday, he will be returning to Iowa, where he won the Democratic caucuses way back in January and has at least two good reasons to revisit now.

Much more than nostalgia seems to have motivated that decision. If things continue to go as well for Mr. Obama this week as they have so far this month, with a romp in North Carolina, a strong showing in Indiana and daily growth in his support among party superdelegates, he could actually end up securing a majority of pledged delegates from nominating contests sanctioned by the party. (To truly become the presumptive nominee, however, Mr. Obama would have to win additional support from superdelegates. And Senator Hillary Rodham Clinton’s efforts to have the party recognize results from two disputed contests, in Florida and Michigan, could also affect the status of the delegate race.)

This achievement will depend in large part on Mr. Obama's performance in the Kentucky and Oregon votes. He has all but conceded Kentucky to Senator Hillary Rodham Clinton, the clear favorite when the race started last year, spending little time there, but is favored in Oregon, where he is making a strong effort.

On Saturday, for example, Mr. Obama appeared at a town-hall-style meeting in the southwestern Oregon town of Roseburg, talking about health care and foreign policy and then taking questions about subjects that included Oregon’s assisted suicide law and domestic partnerships. Implicitly acknowledging what could be at stake in Oregon, he also urged supporters who have voted for him in advance, a common practice there, to make sure that they got their ballots in to tallying centers early enough to be sure they would be counted.