To engage students in the presidential election, a Marymount Manhattan College professor is slated to hold a third presidential straw poll using political buttons. At press time, Kent Worcester, associate professor of political science, was planning to have students in his â??Democracy and its Critics course sell Obama and McCain campaign buttons's as well as independent Ralph Nader and libertarian Bob Barr's to students, faculty and staff on Oct. 22. The first purchase counts as a vote in the straw poll. Each additional sale will go toward the Thomas J. Shanahan Library at the college.