Ballot initiatives to watch this year / AP Photo/Joel Page Voters in every state on Nov. 6 will have the opportunity to influence the trajectory of the nation when they cast their vote for president. In a handful of states, voters can specifically influence history on a few significant issues like marriage, marijuana and genetically modified food. Across 34 states this year, voters will weigh in on 159 ballot initiatives, according to the Initiative and Referendum Institute at the University of Southern California. Here's a look at some worth watching: Same-sex marriage Same-sex marriage has been the subject of legal debate for two decades, but 2012 may be the first year a ballot initiative in favor of same-sex marriage passes. There are four states this November with marriage questions on the ballot. In Maine, Question 1 asks voters, "Do you want to allow the State of Maine to issue marriage licenses to same-sex couples?" Polls show most Maine voters support the initiative, but it could be a close call. Maryland's Question 6 asks voters to uphold a law permitting same-sex marriage that Gov. Martin O'Malley signed in March 2012. A poll from May shows strong support for the law. Similarly, Washington state's R-74 asks voters to either approve or reject the law passed earlier this year that allows same-sex marriage. As of August, the group in favor of same-sex marriage, Washington United for Marriage, had raised a total of $7.4 million for its campaign, the Seattle Times reported. The group opposed to the new law, Preserve Marriage Washington, reported raising more than $525,000. In both Maryland and Washington, the laws in question have yet to be enacted. Lastly, in Minnesota, voters will decide whether to amend the state constitution to define marriage as between one man and one woman. Minnesota currently does not recognize same-sex marriages; the amendment would codify that policy. A Star Tribune Minnesota poll released this week shows 49 percent of Minnesotans favor the amendment while 47 percent oppose it. However, the initiative must win at least 50 percent support to pass. As both sides of the issue feverishly raise money, the question could become the most expensive constitutional ballot question in Minnesota's history, the Star Tribune reported. While half a dozen states and the District of Columbia already have laws permitting same-sex marriage, those laws were put in place by state legislatures or the courts. Over the years, U.S. voters have considered a total of 35 ballot measures banning same-sex marriage, according to the Initiative and Referendum Institute, and all but one of those initiatives passed. The initiative that failed was Arizona's 2006 ballot measure, which would have put limits on civil unions as well as marriage. Public opinion is moving in favor of same-sex marriage -- in 2011, Gallup found for the first time that a majority of Americans supported it -- but the most recent ballot initiative to ban same-sex marriage passed with strong support in North Carolina in May.