The new NBC/Wall St. Journal poll shows Barack Obama opening up a 10 point lead — 52 to 42 — over John McCain. The Democrat’s lead was six points in the same poll two weeks ago.

Interestingly, the biggest factor driving voters away from McCain is not his close ties to George Bush, it’s his choice of Sarah Palin to be his vice presidential nominee:

Palin’s qualifications to be president rank as voters’ top concern about McCain’s candidacy - ahead of continuing President Bush’s policies, enacting economic policies that only benefit the rich and keeping too high of a troop presence in Iraq.

Among voters’ concerns about McCain, “V.P. candidate not qualified” ranked at 34 percent, while “will continue Bush policies” ranked at 23 percent. Dissatisfaction with McCain’s economic policies ranked third with 20 percent.

The poll’s responses about Palin reveal deep concerns among voters:

Fifty-five percent of respondents say she’s not qualified to serve as president if the need arises, up five points from the previous poll.

In addition, for the first time, more voters have a negative opinion of her than a positive one. In the survey, 47 percent view her negatively, versus 38 percent who see her in a positive light.

That’s a striking shift since McCain chose Palin as his running mate in early September, when she held a 47 to 27 percent positive rating.

One of the most often-repeated truisms in presidential politics is that a candidate’s vice presidential choice has little effect on the outcome of the election. Until now, there has been one notable exception to this rule: John F. Kennedy’s choice of Lyndon Johnson helped him win in 1960. Conversely, George Bush’s pick of meagerly gifted Dan Quayle did not prevent Bush from beating former Gov. Michael Dukakis in 1988.

But if the numbers in this poll remain consistent, and McCain loses on Nov. 4, Sarah Palin will achieve a second place in president political history. In addition to being the GOP’s first female vice presidential candidate, she will become proof positive that making a poor choice for vice president can ruin a candidate’s chances in November.