Sen. John McCain, R-Ariz., visiting Boston last week.

AP / LM Otero

WASHINGTON — The process of electing the next president of the United States has reached a critical point: The Democrats and the Republicans, the two major political parties, each have a candidate who party leaders believe will win in November.

On the Democratic side, Illinois Sen. Barack Obama has secured enough delegate votes to wrap up the nomination and become the first African-American to lead a major-party presidential ticket. Obama will be nominated officially in August at the Democratic National Convention in Colorado.

A week later, Republicans will meet in Minnesota and nominate Arizona Sen. John McCain as their standard-bearer. McCain locked up his party’s nomination several weeks ago.

McCain and Obama are friends, but you might not be able to tell that when they’re on the campaign trail. Both will be campaigning hard and spending a lot of money to win in November.

During the summer, McCain and Obama will travel the country, giving speeches about why each thinks he would make the best president. They will concentrate on states where neither man has a clear advantage and thus are up for grabs on Election Day.

Between now and the national conventions, Obama and McCain will each choose a vice presidential running mate. It’s an important job, in part because the vice president takes over if something happens to the president.

At the end of August, Democratic leaders will gather in Denver for their convention, a big meeting during which they will officially nominate Obama and his choice for vice president. There will be lots of confetti, balloons and speeches about how Democrats are the best.

A few days later, the Republicans will meet in Minneapolis-St. Paul to nominate McCain and his running mate. That convention, too, will have plenty of balloons, confetti and speeches saying that Republicans are the best.

After the political conventions, McCain, Obama, their running mates and some minor-party candidates will travel a lot, seeking support from voters.

As the two major candidates, McCain and Obama probably will debate on national television, answering questions from reporters or each other. Then, on Nov. 4, voters will decide who will succeed George W. Bush on Jan. 20 as the 44th president of the United States.