In their countless interviews and speeches before voters, those who seek to replace Barack Obama have given glimpses and outlines of what their top priorities in office would be and who they would appoint to help them turn those ideas into reality.
So what would some of these administrations look like?
If Donald Trump were to win in November, he would be the first man to take the White House without having previously held public office or served at a high level in the military. Because his election would be without precedent, it's difficult to predict what a Trump administration would look like. He has offered some hints, however.He's suggested that Congressman Trey Gowdy, head of the committee investigating the 2012 Benghazi consulate attack, could be his attorney general. (That was before Mr Gowdy endorsed Florida Senator Marco Rubio, however.) He's mentioned that 2008 Republican vice-presidential nominee Sarah Palin would have a place in his presidential cabinet and billionaire financier Carl Icahn is a possible treasury secretary. He's also said he might tap corporate former chief Jack Welsh and investor Warren Buffett as economic advisers.
Mr Trump has generated political shockwaves with his at-times bellicose campaign style and controversial proposals on US border security and a temporary halt on the entry of all Muslims into the US, but he's started offering a more measured, conciliatory tone. This was expected once he grabbed the attention of the world. You may think he ranted about random, offensive subjects but it was no doubt a clever and innovative campaign strategy . He certainly could afford his own personal think tank to come up with a new approach. Now when he speaks with an intelligent, tolerant and logical viewpoint, people give him more credit than is due.
"When I'm president, I'm a different person," he said recently. "When you are running the country, it's a different dialogue that goes. And we can do that easily."
That's been music to the ears of some Republican insiders, who have suggested that a Trump administration may be open to overtures from the party establishment he has often spurned.
Top priorities: Halting illegal immigration, improving border security, policing trade with China.
Mr Cruz has made countless enemies with his fellow Republican politicians, who are unlikely to get plum spots in his administration. Instead, he could look to the activist base and right-wing think tanks to fill out his executive team.
Unlike Mr Trump, Mr Cruz hasn't floated many names of possible high-ranking administration officials. He's mentioned Alabama Senator Jeff Sessions, a former federal prosecutor, as homeland security secretary and said he'd be interested in offering Mr Rubio, a presidential rival, a cabinet position.
He may have fewer top cabinet spots to fill, however, as he's pledged to do away with the departments of energy, commerce, education, and housing and urban development. He's also said he wants to abolish the Internal Revenue Service by switching to a flat income tax.
Before their falling out, Mr Cruz also suggested Mr Trump could help him with trade negotiations and be put in charge of constructing a wall on the US-Mexican border.
Top priorities: Instituting a 10% flat tax, "tearing up" Iran nuclear deal, rolling back Obama administration's healthcare reform.
Mr Rubio has talked about how he presents a "generational choice" for voters seeking a new style of politics and fresh ideas. A Rubio White House, however, would likely be populated by many familiar faces from previous Republican governments. After six years as a US senator, Mr Rubio has strong ties to the party establishment.Mr Rubio's campaign staff is full of veterans of Mitt Romney's 2012 presidential campaign and others in the Republican Party hierarchy. Many of his advisers, particularly on foreign policy, are old Republican hands like author Robert Kagan and throwbacks to the George W Bush administration, including Elliott Abrams and Stephen Hadley.
In a November 2015 interview he told the Wall Street Journal's Gerard Baker that he would use his "political capital moral clarity" and do "everything possible to ensure that America fulfils its potential in a 21st Century economy". He went on to mention a laundry list of actions, including re" as a newly-elected president to "give our nation a clear foreign policy with forms to the tax structure, energy policy, government regulations, entitlements and healthcare.
Top priorities: Increased funding for the military, higher education "modernisation", end the Obama administration's moves to normalise relations with Cuba.
Three of the senior policy advisers on her campaign team are Maya Harris, a foreign policy think-tank veteran, and Ann O'Leary and Jake Sullivan, both of whom have previously served on her staff. Alan Blinder, a former vice chairman of the Federal Reserve and a Princeton University professor, is her chief economic adviser. Her campaign chair, John Podesta, served as chief of staff to President Bill Clinton and as an adviser to Mr Obama.
Mrs Clinton said during her campaign kick-off speech in June that her administration would be defined by "four fights" - to make the economy work for "everyday Americans", to ensure US security, to strengthen US communities and to end political "dysfunction".
At the most recent Democratic debate, Mrs Clinton detailed her top three goals for her first 100 days as president.
She mentioned job-creation and infrastructure programmes, raising the minimum wage and "guaranteeing finally equal pay for women's work". She also said that she would expand Mr Obama's healthcare reform, including lowering the costs of prescription drugs.
Top priorities: Criminal justice reform, college affordability, comprehensive immigration reform.
Bernie Sanders has been clear about the kind of people he doesn't want in his White House."My cabinet would not be dominated by representatives of Wall Street," he said during a television interview last July. "There are a lot of great public servants out there, great economists who for years have been standing up for the middle class and the working families of this country."Past Democratic and Republican presidents have frequently turned to New York financial market insiders as economic advisers, including Jack Lew for Mr Obama, Henry Paulson for Mr Bush and Robert Rubin for Mr Clinton.
By contrast, Mr Sanders mentioned New York Times economic columnist Paul Krugman, former Clinton administration labour secretary Robert Reich and Columbia University economist Joseph Stiglitz as the kind of economic advisers he'd seek out.
When asked what his first 100 days as president would look like, Mr Sanders said he would push to enact universal healthcare, raise the minimum wage to $15 an hour and increase investment in infrastructure.
"What my first days are about is bringing America together to end the decline of the middle class, to tell the wealthiest people in this country that, yes, they are going to start paying taxes and that we are going to have a government that works for all of us and not just big campaign contributors."
Top priorities: Raising taxes on the wealthy, breaking up large financial companies, free college education for all Americans.
Many thanx to Anthony Zurcher for material