Democrat Hillary Clinton has pulled ahead of Republican Rudy Giuliani in a new nationwide poll, but a new look at Democrats in Iowa shows she is no shoe-in for her party's nomination.

The latest Gallup/USA Today poll shows the New York senator is supported by 50 percent of Democrats and Democratic-leaning independents nationally.

Twenty-two percent support Illinois Sen. Barack Obama and 15 percent back former North Carolina Sen. John Edwards.

On the Republican side, Giuliani's support holds steady at 34 percent nationally, the poll found. Arizona Sen. John McCain is now second with 18 percent, and former Tennessee Sen. Fred Thompson is at 17 percent. Former Massachusetts Gov. Mitt Romney trails with 14 percent.

And in a Clinton-Giuliani race, Clinton leads 51 percent to 45 percent.

The latest AP-Ipsos reflected similar national support for Clinton, giving her a 2-to-1 lead over her nearest rival, Obama.

Clinton was ahead of Obama 45 percent to 22 percent, about the same as her margin last month. Edwards had 12 percent.

Giuliani enjoyed a slight advantage over Thompson, by 29 percent to 19 percent. That was statistically about the same as the 27 percent to 23 percent advantage Giuliani held last month.

The survey showed a Republican race that remains competitive, with Giuliani so far not pulling away from the pack. Thompson, criticized for a slow-starting campaign, has yet to move beyond the one-fifth of GOP voters he has been able to attract so far.

Three other Republican candidates stayed roughly where they were a month ago. McCain had 13 percent, Romney had 12 percent and Huckabee had 10 percent.

Iowa Tells Different Story

Her national polling may show a wide lead, but Clinton is barely leading among party faithful in Zogby's latest Iowa poll.

She has 28 percent support among likely Democratic caucus-goers, down from 30 percent in an August.

Obama has moved up to 25 percent, up from 19 percent in August. That puts him within the poll's plus or minus 4.5 percentage-point margin of error.

The telephone poll of 502 likely Democratic caucus-goers statewide was conducted Nov. 6.

Edwards remains in third place with 21 percent in the Zogby poll, down a bit from late summer.

Asked whether former President Bill Clinton would have a negative or positive impact on a Hillary Clinton presidency, should one come to pass, 79 percent of respondents said his impact would be positive, Zogby found.

Among likely GOP caucus-goers, Romney remains far ahead of the rest of his party's field in Iowa, even though he lost two percentage points since May, Zogby said.

Romney, with 31 percent, is far ahead of former Arkansas Gov. Mike Huckabee's 15 percent support. Giuliani has 11 percent and former Tennessee Sen. Fred Thompson has 10 percent. Arizona Sen. John McCain has 8 percent support.