Old-fashioned hand-shaking and crowd-pleasing in a state where the biggest city, Billings, has a population of about 105,000 are likely to determine the outcome.

North Dakota

Once expected to move into Republican control, the seat held by retiring Senate Budget Committee Chairman Kent Conrad, a Democrat, has turned this small state into a political combat zone.

Democrat Heidi Heitkamp, a former attorney general who’s seasoned in statewide races, is credited with running an energetic campaign against freshman Republican U.S. Rep. Rick Berg. Berg stays close as he hammers the unpopular Obama.

Virginia

Two former governors are competing in a state that’s already getting lots of attention because it’s a presidential-race tossup.

Democrat Tim Kaine has pulled slightly ahead in most polls, but Republican George Allen has won statewide twice before, for governor in 1993 and Senate in 2000. Virginia is hard to handicap, since demographics are changing rapidly as northern Virginia counties attract more professionals who’ve been trending Democratic. Turnout for Obama or Romney could make the difference here.

Nevada

UNLV’s Damore described the race as a choice between unpopular alternatives. Incumbent Republican Sen. Dean Heller has been slipping; his 9-percentage-point lead in July’s Rasmussen poll shrank to 1 last week.

Democratic U.S. Rep. Shelley Berkley has faced ethics questions over her efforts to affect federal involvement in kidney health policy. Her husband is a well-known Las Vegas nephrologist. Berkley has said her interest was ensuring quality health care for her constituents.

Nevada’s economy has been as dismal as any state’s in the nation, but what might make the difference are immigration issues, particularly since 15 to 20 percent of the vote may come from the Latino population. Polls have differed on which candidate has more support among Hispanics.

Massachusetts

Democrat Elizabeth Warren led incumbent Republican Sen. Scott Brown by an average of 2.4 percentage points in polls taken last week, according to RealClearPolitics, a website that compiles such data.

Warren has been gaining slowly, and David Paleologos, the director of the Suffolk University Political Research Center, attributed her progress to Democrats warming to the fiery consumer advocate. Brown faces another problem: Though Romney is a former governor of the state, he isn’t particularly popular. Last week’s Suffolk poll found Obama ahead by 64-31 percent.

Massachusetts voters, though, are known for embracing moderate Republicans, and the poll found that half liked the idea of bipartisan representation in Washington.

Brown has been careful to keep a distance from Romney. “I’m Scott Brown. He’s Mitt Romney,” he said. “People know who I am. I’ll let my record speak for itself.”

In the other Senate races being watched, turnout for the presidential election could make a difference. In Connecticut, for instance, the Sept. 11-16 University of Connecticut/Hartford Courant poll had Obama up by 21 percentage points. Yet Republican Senate candidate Linda McMahon trailed Democratic U.S. Rep. Christopher Murphy by only 4.