Former New York City Mayor Rudy Giuliani (R) leads Arizona Senator John McCain (R) by eighteen points in the race for the Republican Presidential nomination. Giuliani now attracts support from 33% of those likely to vote in a Republican Primary. That’s consistent with his level of support for three of the past four weeks, but down from a spike to 37% last week.

McCain slipped another point last week and is supported by just 15% of those surveyed. That is the lowest level of support measured so far for a man recently was presumed to be the frontrunner for the nomination. Thirteen percent (13%) now support former House Speaker Newt Gingrich (R) while 10% prefer former Massachusetts Governor Mitt Romney (R). No other Republican attracts more than 2% support at this time.

Rasmussen Reports releases updated polling data on the Republican nominating contest every Tuesday. Results for the Democrats are updated on Mondays.

Among the 31% of Likely Primary voters who identify themselves as Very Conservative, Gingrich has a statistically insignificant lead over Giuliani. Romney is third among the Very Conservative while McCain is fourth.

Those who identify themselves as Somewhat Conservative prefer Giuliani over McCain by a 37% to 17% margin. Among political moderates in the GOP, 42% say they would vote for Giuliani, 20% for McCain, and 6% for Romney.

A separate survey found that 50% of all Americans voters would definitely vote against Gingrich if he is on the general election ballot. Just 20% would definitely vote for him.

Giuliani is the only candidate in either party who more people would definitely vote for than against. He also currently leads all Democrats in General Election match-ups. This includes Senator Hillary Clinton, Senator Barack Obama, former Senator John Edwards, Governor Bill Richardson, and Senator Joe Biden.

McCain is essentially even with Clinton, Obama, and Edwards while leading Richardson and Biden.

Romney trails Clinton, Obama, and Edwards. Other GOP hopefuls also trail Democrats in General Election polling.

The current survey is based upon national telephone interviews with 599 Likely Republican Primary Voters conducted March 12-15, 2007. The margin of sampling error is +/- 4 percentage points with a 95% level of confidence.

See a summary of all match-ups along with favorability ratings and perceptions of the candidates’ ideology. A summary is also provided for Democratic contenders.