With less than three months to the US election day, neither Hillary Clinton nor Donald Trump is shifting to the ideological centre.

It's a break from modern presidential campaigns that's being driven by the decline of swing voters.

In a speech last Friday, Clinton again emphasised her progressive stances on economic issues such as raising the minimum wage, tuition-free public college, expanding Social Security, adding a public insurance option to the Affordable Care Act, and cracking down on Wall Street.

She also drew wide praise from liberal activists by promising to oppose the Trans-Pacific Partnership trade pact.


"She continues to run on the same set of progressive issues she discussed in the primary," Clinton campaign spokesman Brian Fallon said. "That is not at all a hindrance on her ability to reach out to independents and Republicans because, on issues from college affordability to a minimum wage increase to gun safety, her proposals are perfectly reasonable, fully paid for, and enjoy a consensus level of support."

And Trump has reaffirmed his nativist, "America-first" brand of politics since accepting the Republican nomination, rousing crowds at his rallies by vowing to build a Mexico-funded wall along its border with the US and stop the flow of illegal immigration.

He has promised to confront Mexico and China with aggressive trade restrictions on products exported to the US, ban immigration from "terrorist countries," revisit US commitments to protect Nato allies, and pursue a multi-trillion-dollar tax cut with the largest benefits estimated to go to the wealthiest Americans.

Trump rebuffed a report in the New York Times that he's promised to soften his views on the advice of advisers as the election draws closer. "False, I am who I am," he tweeted on Monday. He told CNBC on Friday that his plan in the final stretch is to "just keep doing the same thing I'm doing right now, and at the end it's either going to work or I'm going to have a very, very nice, long vacation".

The policy retrenchment is a change from the pivot presidential candidates traditionally have made towards the political centre after locking up their nominations through a series of primaries and caucuses that typically attract loyal party members further from the ideological centre.

In 2012, after securing the Republican Party's nomination, Mitt Romney downplayed his plan for upper-income tax cuts, softened his rhetoric against government regulations, and promised to cover pre-existing medical conditions despite proposing to repeal Obamacare.

In 2008, Democratic nominee Barack Obama proposed to expand faith-based initiatives and backed away from an earlier stance on civil liberties by voting for a bill that continued government surveillance programmes.

But as Romney learned, the importance of the independent voter can be overstated. He won independents 50 per cent to 45 per cent, according to exit polls, but lost the election handily to Obama.

The change this cycle is partly structural, propelled by party polarisation and fewer persuadable voters.

A 2015 study by Michigan State University political scientist Corwin Smidt found that the share of US "floating" voters (as opposed to those who stick with a party) has fallen to 5 per cent from a high of roughly 15 per cent in the 1960s, even though more voters lay claim to being "independent".

"Presidential campaigns have become more about base turnout with a particular focus on sporadic voters that need to be motivated to turn out," said Ben LaBolt, a Democratic strategist who served as national press secretary for Obama's re-election campaign.

"Persuasion for the sliver of the electorate in the middle still matters to some degree, and there's an opportunity for Clinton on that front in this election. But the mobilisation of the Obama coalition will be most important."

The unique dynamics of the 2016 election are also a factor.

"Trump's orientation towards the election is based on the perspectives of an insurgent candidacy," John Petrocik, a political scientist at the University of Missouri who studies voting behaviour, said.

"I would not have expected him or [former Democratic candidate Bernie] Sanders to appeal to the median voter. They are insurgents who are mobilising what they view(ed) as an ignored majority."

Rather than courting the middle, Trump's strategy relies on upending the electoral map and winning over previously Democratic white voters in states like Pennsylvania, Wisconsin, and Michigan by lambasting trade pacts like Nafta as the reason thousands of working class Americans have been displaced from their jobs.

Trump, 70, has invited left-leaning supporters of Sanders, who also made anti-trade sentiment a centerpiece of his campaign, into his coalition by pointing out that Clinton, 68, supported the TPP in 2012, as Obama's Secretary of State, before coming out against it in her campaign.

"Clinton 'pivoted' to Sanders because of the latter's success in the primary season," Petrocik said. "Clinton is not moving towards Trump because he does not appear to be have success, and Trump is not altering his approach because he is an insurgent who believes (probably incorrectly) that he will be successful."

Part of Clinton's strategy in pushing her progressive message, said anti-Trump Republican strategist Stuart Stevens, an adviser to Romney in 2012, is to block "any drift to Trump from Sanders voters".

He added: "I think on election day, Trump will get as many Sanders voters as Lena Dunham fans who subscribe to Guns and Ammo".

The Republican base is much further from the centre than the Democratic base. So Trump has to pivot to win. Hillary does not and should not


Clinton's actions indicate that she believes she can pick off moderate Republicans from Trump without making policy concessions.

She has aggressively courted prominent Republicans by contrasting her optimistic outlook with Trump's darker vision, claiming that the real-estate developer and TV personality is unfit to be the leader of the Free World.

Numerous Democratic strategists say embracing a progressive platform is key to reassembling the Obama coalition, which includes nonwhite voters, unmarried women, and millennials, and which powered the president to two decisive victories.

"The universe of so-called swing voters has been getting smaller with every election," said Dan Pfeiffer, a former senior adviser to Obama.

"There is an asymmetry between the parties; the Republican base is much further from the centre than the Democratic base. So Trump has to pivot to win. Hillary does not and should not."

- Bloomberg