Herman Cain got a lot of attention when a poll from Zogby showed him with a 20-percentage-point lead over his closest Republican presidential rival last week. It is a sign of popularity among likely voters, but Americans for the most part don't know much about him or the rest of the GOP field.

A little less than one-half of Americans could name a single candidate running for president, with just 28 percent mentioning Texas Gov. Rick Perry and only 27 percent naming former Massachusetts Gov. Mitt Romney, according to a Pew Research Center poll from Tuesday.

The campaign season is starting to intensify: The Iowa caucuses are a little less than three months away.

However, comparing voters' awareness now with their awareness at about the same time in the campaign season four years ago is revealing. Back then, 59 percent of Americans could name at least one 2008 GOP presidential candidate.

In October 2007, 45 percent could name former New York Mayor Rudy Giuliani, and 30 percent could name Romney.

And for all of Cain's newfound popularity in the polls, only 9 percent of respondents in the Pew poll mentioned the former Godfather's Pizza CEO as one of the candidates. The poll was conducted with an open-ended question asking respondents to name as many presidential candidates as they could.

When Pew asked Republicans and like-minded Independents to name a candidate, a more robust 66 percent could do so, but Cain was the answer 15 percent of the time, putting him in fourth place behind U.S. Rep. Michele Bachmann of Minnesota.

Meanwhile, among likely Republican primary voters, Cain seems to be leading or in the same league as his GOP rivals.

The Zogby poll from Thursday said Cain held a 20-percentage-point lead over his closest Republican rival, blowing away Romney's 18 percent among primary voters. Perry and U.S. Rep. Ron Paul of Texas were tied with 12 percent each.

For all likely voters, Cain even pulled ahead of President Barack Obama, 46 to 44 percent, with a 3.5 percent margin of error. Obama holds Romney and Perry to 40 percent each among likely voters, the Zogby poll said.