It turns out Barack Obama was wrong: Hillary Clinton isn't likeable enough, some Democrats are fretting.

Top Democratic advisors and consultants are warning that the Democratic frontrunner's chief obstacle is her own personality, or at least how voters perceive it, after a year of relentless criticism from right and left.

'I bring it down to one thing and one thing only, and that is likability,' Democratic pollster Peter Hart told the Washington Post, which collected a string of similar sentiments from Clinton allies.

Clinton's likeability numbers are lower than they were at the start of the campaign, notwithstanding countless efforts by her team to boost her numbers through advertising, soft interviews, and warm chats in diners and living rooms around the country.

Her allies raise concerns that Clinton is 'scripted and thin-skinned.' That could be a problem going against a candidate as improvisational as Donald Trump.

'She's horrible at running, but she's fantastic at governing,' a longtime friend and supporter told the paper. 'She will roll up her sleeves. That's not just a campaign talking point.'

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Too scripted? Clinton allies worry that the 'likeability' problem is her greatest concern

But Trump plans to go after Clinton both on personality and her record, with hits on the Benghazi attack and the chaos in Libya meant to eke away at her judgement.

That might help him weather attacks on his own perceived character flaws, like a weekend New York Times report that dug through his past private treatment of women he dated.

'What I want to happen are things that will never happen,' a longtime Clinton family supporter and donor lamented. 'I mean, we can't give her an injection to make her an energetic candidate.'

Clinton was challenged on the likeability issue during a New Hampshire debate in the 2008 campaign.

'Well that hurts my feelings, but I'll try to go on,' Clinton quipped – showing a flash of the humor that close friends say she often shares in private. 'You're likeability enough, Hillary,' then-Senator Barack Obama interjected dryly.

The Democrats are hardly in hopeless straights. Early analysis is already revealing Clinton's built-in advantage in the electoral college, where Trump must win in battlegrounds like Ohio and Florida to prevail.

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NBC's early electoral college forecast puts the Democrats on track to win 253 electoral votes at the outset and Republicans set to take 190 in the battle to reach 270 electoral votes.

And Trump could prove to be even more unlikeable once he gets in front of an electorate consisting of Democrats and Republicans.

'They're dealing with 20 years, almost 30 years now, of public narratives about her,' Dan Pfeiffer, a former top Obama advisor, said. 'I don't think that's fixable in the next six months. You have to turn it from a referendum on her trustworthiness to a contrast.'

Clinton's own pollster, Joel Benenson, is hardly declaring victory.

'Hillary Clinton is in a stronger position than Donald Trump, but it will be competitive,' Benenson said. 'All these races are.'

A HuffPost pollster average last month had Clinton's unfavorability at 55 per cent, compared to a 40 per cent favorability rating.

Pollster Peter Hart: 'I bring it down to one thing and one thing only, and that is likability'