Israel has become a major factor in the upcoming mid-term elections, with Democratic candidates being forced to defend President Obama's Middle East record and occasionally dissociate from him entirely.

It first became clear that Israel was going to be a weak spot for the Democrats several months ago, when Congressman Henry Waxman, undoubtedly the senior and most powerful Jewish lawmaker in the House of Representatives, published a piece in the Los Angeles Jewish Journal denying that the president had mistreated the Jewish state.

"No, President Obama is not a Muslim; he is a Christian. No, Prime Minister Netanyahu did not enter the White House through a back entrance," Mr Waxman wrote, going on to counter other widespread myths that portray the president as unfavourable towards Israel.

He was prompted, he said, by the unprecedented number of phone calls and emails from Jewish voters, all expressing concern at President Obama's attitude to Israel.

Mid-term elections, in which voters get to choose all House members and a third of the Senate seats, usually centre on domestic issues. What a congressman has done for his district is usually far more important than what the president thinks of a foreign nation.

In addition, polls have traditionally shown that Jewish voters do not view Israel as a decisive factor when they go to the polls.

But in this year, President Obama's initial bumpy beginning with Israel is being seen as a liability for Democrats running in areas with a large Jewish population, and Republicans are quick to accuse rivals of not being supportive of Israel.

A Gallup poll published last week shows that Mr Obama's job approval amongst Jews is at 61 per cent, down from 77 per cent in the first half of last year.

A new group, the Emergency Committee for Israel, has been paying for TV ads across the country that question some left-leaning Democrats' support for Israel.

In Pennsylvania, candidates are struggling to prove their pro-Israel credentials in a close Senate race.

Democrat Joe Sestak was accused of not being supportive of Israel because he signed a congressional letter in January calling for an easing of the Gaza blockade.

Ads on local TV stations and online forced the Democratic candidate to spend time and campaign money in attempts to refute the concerns.

Similar ads, targeting Democrats who signed the Gaza letter, ran in Ohio, Connecticut and Virginia.

Even in Southern Florida, Jewish Congressman Ron Klein has found himself engaged in a battle to dispel accusations made by his Republican rival arguing Mr Klein is not a strong enough supporter of Israel.

Mr Klein, like many other Democrats in close races, has made an effort to highlight his disapproval of President Obama's approach to Israel in his early months in office.

"I criticised President Obama at the time when I thought there was an over-reaction on the settlement issue," said Mr Klein. "I thought that he spoke about it in the wrong way and that the focus was wrong. And in a face to face meeting I let him know that."

Mr Klein and other Democrats, however, stressed that over the past six months relations between the Obama administration and Israel had dramatically improved.