With New Hampshire’s first-in-the-nation primary set for Tuesday, betting markets overwhelmingly expect President Trump to win the Granite State primary and go on to win the GOP presidential nomination.

Although betting on the outcome of American political elections is illegal in America, political betting markets allow people living in countries where it is legal to wager on predictions of the outcomes of major political events.

One such website, PredictIt, allows bettors to buy shares predicting that a certain event will come to pass, such as Mr. Trump winning the New Hampshire primary. Each share, bought for less than a dollar, will pay out with a dollar if the prediction proves accurate. Users may also trade these shares like stocks as the price rises and falls.

Some analyses have found that betting markets are more accurate predictors of the outcomes of elections than polls. One analysis of the 2008 and 2012 elections found that bettors were better than pollsters at handicapping elections.

An anthropologist at the University of Birmingham, Anthony Pickles, writes for the Conversation that betting markers also “react faster than the snappiest snap poll.”

“The political gambling community itself would turn a pollster’s stomach,” Mr. Pickles writes. “I have found it to be overwhelmingly made up of white, educated males who are mathematically inclined and politically sophisticated (including a good number of politicians themselves).”

At the time of writing, a share predicting that Mr. Trump will win the New Hampshire GOP primary is trading at 95 cents, which is up about 12 cents from January 15, the day of the Iowa caucuses.

A share predicting a win by the last remaining GOP challenger to Mr. Trump, Ambassador Nikki Haley, is currently trading at seven cents, down 16 cents from its peak on January 16.

While Ms. Haley has been seeking to make the competition into a two-person race since before the Iowa caucuses, polling indicates that Mr. Trump is favored to win even in a state like New Hampshire, which is relatively favorable to Ms. Haley compared to other states.

FiveThirtyEight’s average of polls in the state has Mr. Trump polling at about 51 percent support and Ms. Haley polling at about 37 percent.

Bettors have also become more convinced that Mr. Trump will become the eventual nominee for the Republican Party, with shares predicting Mr. Trump’s nomination now trading at 90 cents, up six cents from January 15.

Shares predicting Ms. Haley winning the nomination are now trading at nine cents, one cent below where they were trading on January 15.

While bettors appear to predict that the GOP primary will be all but over after the results of the New Hampshire primary are in, bettors see a more competitive competition in the contest to become Mr. Trump’s vice presidential pick.

Bettors see Congresswoman Elise Stefanik and Governor Noem of South Dakota as the favorites. Shares predicting Ms. Stefanik as Mr. Trump’s running mate are trading at 23 cents, and shares predicting Ms. Noem in the spot are trading at 21 cents.

A senator of South Carolina, Tim Scott, is the third favorite, according to PredictIt, with shares predicting Mr. Scott being chosen trading at 15 cents.