Republican presidential hopeful Newt Gingrich is leading the field after potential rivals stumbled in recent weeks, according to a national survey.

The most recent PPP poll of likely GOP voters shows Gingrich up 13 percentage points in the past month, in the lead at 28 percent. The same poll puts Hermain Cain in second at 25 percent, and former Massachusetts Governor, Mitt Romney, third at 18 percent.

Rick Perry is at 6%, Michele Bachmann and Ron Paul at 5%, Jon Huntsman at 3% and Gary Johnson and Rick Santorum each at 1%.

While Gingrich is up 13 points compared to a month ago, Cain has dropped by 5 points and Romney has gone down by 4. Support for Cain, who has been affected by allegations of sexual harassment, has seriously reduced.

Cain's base of strength continues to be with Tea Party voters, where he gets 33% to 31% for Gingrich, and only 11% for Romney. The other Republican coming off a bad week is Rick Perry and his numbers have continued on their downward trajectory. Regrading Romney he has not shown any ability to take advantage of the trouble his fellow candidates keep getting themselves into.

The PPP poll of 576 Republican primary voters has a margin of error of plus or minus 4.1 percentage points.

Gingrich has been rising steadily over the last two months and now leads the Republican field nationally, Dean Debnam, president of Public Policy Polling said in a press release. The top has proven to be a dangerous place in this GOP race, though, and we'll see if he can sustain it for very long.