As the primary race winds down, the campaigns of both front runners for their parties' nomination are zooming in on the main event itself in November with a shift in focus involving everything from changing the tone of the message to more mobilisation on the ground.
Already, on the Democratic side, former secretary of state Hillary Clinton has been focusing her attacks on her Republican rivals and less so on her Democratic opponent, Vermont senator Bernie Sanders. As for the Republicans, Mr Donald Trump has adopted a slightly more presidential tone during major announcements.
In the 2008 presidential polls, where there was no incumbent in the race - like this cycle - 131.4 million people (56.9 per cent of the voting-age population) cast their ballots, according to the Pew Research Centre. This was more than twice the number of primary voters picking their party nominee then.
With this in mind, candidates would try to appeal to a larger cross-section of the party base as they move from the primaries to a general election campaign.
Associate professor of political science Dan Franklin from Georgia State University said Mrs Clinton will have to "reach out to Sanders voters by co-opting some of his issues". On the other hand, independent voters are more moderate than Sanders voters, so she can attract them by "highlighting many of Donald Trump's extreme positions".
Dr Franklin added: "In a two-party, winner-takes-all system you can win by getting out your own voters... but just as effective is to discourage your opponent's voters from participating through negative campaigning."
One issue Mrs Clinton might have to tone down on is gun control, said associate professor David Karol from the University of Maryland. "Hillary has talked a lot about gun control but she may put less emphasis on it in the general (election), because the key to the general is always winning swing voters and those tend to be white voters," he said. Whites favour gun rights more than others, surveys show.
Still, experts believe Mr Trump is in a more difficult position.
Dr Franklin said: "If he begins to behave as a more 'establishment' candidate, he might lose his core supporters. On the other hand, if Trump continues to campaign as he has in the primaries, he risks losing broad sections of the electorate such as women and minorities."
The tycoon's campaign is no doubt experimenting with a more presidential style - Mr Trump used a teleprompter to avoid misspeaking during a major foreign policy speech last Wednesday and also refrained from some of his more controversial catch phrases like "building a wall" to stop illegal immigrants from entering the US.
Some experts say what both candidates have to work on is their "likeability". "Never before have the two parties nominated presidential candidates with such high unfavourability ratings," said associate professor of political science Melissa Miller from Bowling Green State University.
An average of favourability rating surveys done by political website Real Clear Politics shows 65.4 per cent of voters look at Mr Trump unfavourably against 28.4 per cent who are favourable towards him.
Mrs Clinton has a similar problem, although with a narrower margin: 38.4 per cent of voters feel favourably towards her, compared with 54.9 per cent who do not.
Dr Miller said the campaigns can employ certain tactics to remedy the problem of likeability, for example by publicising endorsements from well-liked and widely regarded individuals.
"There are certain strategies Clinton and Trump may try in the coming months, but Trump especially has a lot of ground to make up," she added.
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