A week after the Iowa caucuses which ended up in a virtual tie at the top between Mitt Romney and Rick Santorum, U.S. Republican presidential hopefuls kick off their second contest in New Hampshire on Tuesday. Here are five things to watch in the first-in-the-nation primary.

No. 1: Will Romney win beautifully?

After winning by the skin of his teeth in Iowa, Romney is the favorite to win handily in New Hampshire.

"It will be a stunning blow to his campaign if he doesn't win New Hampshire," William Galston, senior fellow at the Brookings Institution, told Xinhua. "The only question is the margin."

Romney views New Hampshire as his impregnable fortress. He has invested a lot more time in the state than he ever did in Iowa. It will be difficult for any of his opponents to beat him in what's considered his second home state. He was a former governor of Massachusetts which is next door to New Hampshire. And more importantly, he has been for months enjoying wide lead over the field in the Granite State in major polls.

According to a Public Policy Polling (PPP) survey released Sunday, Romney is holding 35 percent of support among likely Republican voters in New Hampshire, 17 points ahead of Texas congressman Ron Paul who followed at 18 percent.

Still, Romney has seen his support somewhat eroded over the past week, which came along with the surges of Paul, Jon Huntsman and, to a lesser extent, Rick Santorum.

It might be seen as another ugly win, as he did in Iowa, if he ends up winning by a single-digit margin Tuesday night.

No. 2: Will Santorum build on Iowa success?

The former Pennsylvania senator was mostly marginalized in this campaign until two weeks into the Iowa caucuses, in which he came in second with just eight votes short of Romney.

Riding the momentum, Santorum has seen his poll numbers rising in some key battlegrounds like New Hampshire and South Carolina. He is considered one of the candidates that could potentially coalesce the conservative votes -- now fragmented among several candidates -- to pose a real challenge to Romney.

But it would be difficult for Santorum to turn New Hampshire into another Iowa given the demographic difference of the two states.

The Republican party in Iowa is dominated by evangelicals and social conservatives, so that Santorum's extremely conservative message on abortion, same-sex marriage and other social issues worked well there. New Hampshire is more secular and less conservative, with economy and jobs topping people's concerns.

"It's harder to have social conservatives to do well in New Hampshire, and they have never done well there," said Galston of the Brookings Institution. "I don't expect Santorum to break that."

Santorum ranks fifth in the PPP survey with 11 percent of the votes, essentially tied with former House Speaker Newt Gingrich who is at 12 percent.