Just why is President Barack Obama enjoying the support of US Muslims, while Christians are among those who least approve of his leadership?

A new Gallup poll has found that 72 per cent of American Muslims gave Obama job approval during the first half of 2014, while Christian groups offered him a far lower rating.

Just 37 per cent of Protestants approved of the President's work, matched by 44 per cent of Catholics and a dire 18 per cent of Mormons.

Even of those who identified themselves as of no religion, just 54 per cent said Obama has done a good job so far this year.

"The patterns in Obama's job approval by religion have prevailed throughout his presidency, with Muslim, Jewish and nonreligious Americans giving him higher ratings, and Mormons and Protestants giving him the lowest ratings," Gallup stated.

"The United States remains a predominately Christian nation, with roughly half of Americans identifying with a Protestant religion and another quarter identifying as Catholics. Thus, the opinions of these Christian groups are by far the most influential in determining Obama's overall ratings."

Obama has frequently faced condemnation in the past from those who question the validity of his professed Christian faith – some have even branded him "the first Muslim President".

Startlingly, 17 per cent of Americans said they believed Obama was a Muslim in a 2012 survey – a figure which equates to almost one fifth of the entire population.

Jim Wallis, who currently works as spiritual advisor to the President, however, has previously leapt to Obama's defence in light of these allegations.

"Let's set the record straight. I have known Barack Obama for more than 10 years, and we have been talking about his Christian faith for a decade," he wrote in a 2008 blog.

"Like me and many other Christians, he agrees with the need to reach out to Muslims around the world, especially if we are ever to defeat Islamic fundamentalism. But he is not a Muslim, never has been...[He] gave his life to Christ in a very personal and very real Christian conversion experience."

Wallis also lambasted those who attack the President's faith: "Like his politics or not, support his candidacy or not – but don't disparage Barack Obama's faith, his church, his minister, or his credibility as an eloquent Christian layman who feels a vocation in politics," he urged.

"Those falsehoods are simply vicious lies and should be denounced by people of faith from across the political spectrum."

The latest Gallup poll will come as no surprise to many, however. The President has long been subject to criticism by conservative Christian groups who oppose many of his social policies surrounding such issues as abortion, birth control and gay marriage.

Over 100 conservative religious leaders recently signed a letter in which they implored Obama to add a conscience clause to legislation which will better protect religious freedom for those of faith.

Christians are typically aligned with the Republican movement in the US, while Muslims, interestingly, are "heavily Democratic", according to the Washington Post.

Research indicates that 63 per cent of US Muslims lean to the left of politics, while just 11 per cent position themselves to the right.