Voters across Maine, Nevada, South Carolina and North Dakota head to the polls Tuesday for another day of primary elections in America, but much of the political world will be focused on Maine's high-stakes U.S. Senate contest.

Graham Platner is seeking to make a Democratic nomination for U.S. Senate official in advance of one of the most anticipated contests of the year.

Primaries for U.S. Senate and U.S. House on Tuesday will set the stage for a midterm general election in which Maine is expected to play a critical role in deciding control of both chambers.