Bernie Sanders beats Joe Biden in national polls as candidates clash over social security

Bernie Sanders leads all other candidates seeking the Democratic nomination for president and is the most likely candidate to beat Donald Trump, according to two polls that place the Vermont senator as the top contender as the Iowa caucus and early state primaries near.

In a CNN poll, 27 per cent of Democrat and Democrat-leaning independents support Mr Sanders as the Democratic nominee. Twenty-four percent of respondents support former Vice President Joe Biden. Both candidates polled double digits ahead of other forecasted front-runners Elizabeth Warren and Pete Buttigieg.

Though the CNN poll puts their neck-and-neck support within the margin of error, it's the first time that Mr Biden has fallen from a clear lead in a CNN poll.

The results arrive as Mr Sanders and Mr Biden spar over the former vice president's previous comments on social security, as video resurfaced of Mr Biden endorsing controversial spending cuts to the program.

In a campaign video, Mr Biden accused Mr Sanders of launching a "barrage of negative attacks" against the candidate while he refused to answer questions about his past support for those cuts.

Results of the CNN poll show that Mr Sanders spiked seven percentage points over the last month following a similar December poll asking voters to pick their choice for the Democratic nominee.

The poll was conducted by SSRS from 16 January though 19 January among a random national sample of 1,156 people with an oversampling in battleground states.

Mr Sanders also claims the highest percentage of voters — 38 per cent — who said they would be "enthusiastic" about his nomination, rather than merely "satisfied" or "dissatisfied" or "upset".

Among the highest in the "satisfied" category, 42 per cent of respondents said they would be "satisfied but not enthusiastic" about Ms Warren's nomination, but only 29 per cent said they were "enthusiastic". Amy Klobuchar captured 40 per cent for "satisfied but not enthusiastic" and only 19 per cent for "enthusiastic".

Mr Sanders also is the candidate that most respondents said agrees with them on issues that matter most to them (at 30 per cent) as well as the candidate that understands the problems facing people like them (at 29 per cent).

He also has the largest support among non-white respondents (30 per cent) as well as white respondents (24 per cent).

The senator also leads against the incumbent president by the widest margin among the Democratic candidates when voters are asked to choose between two candidates in a hypothetical face-off in the general election, according to the results of a SurveyUSA poll.

In the SurveyUSA poll of 4,069 registered voters nationwide, Mr Sanders had a nine-point lead at 52 per cent to Mr Trump's 43 per cent.

Mr Biden was the runner-up, with the former vice president getting 50 per cent to Mr Trump's 43 per cent.

For a similar question in the CNN poll, only 24 per cent of respondents said Mr Sanders has the greatest chance of defeating Mr Trump in the general election. He came in second to Mr Biden — 45 per cent of respondents said he is the best chance of beating the incumbent.

The CNN poll also shows that 41 per cent of respondents believe Mr Biden is the Democrats' best hope of "uniting the Democratic party". Mr Sanders came in second, with only 16 per cent of respondents.