Iowa Republicans will caucus this evening in the wake of a startling turnaround in the electoral fortunes of John McCain. A new poll from Pew Research places the Arizona senator, whose chances have been written off repeatedly in the last 12 months, as the national Republican front-runner for the first time in a year.

More good news emerged for Mr. McCain in New Hampshire, which holds its primary January 8 and where a new poll from Suffolk Tracking shows him surging nine points ahead of Mitt Romney, who has been the front-runner there since May.

RELATED: Arizona Senator Is Upbeat in Iowa

The re-emergence of the 71-year-old Mr. McCain as a leading candidate for the Republican presidential nomination has obliged campaign managers and political commentators to reassess how the GOP race will unfold.

Until this week, it was widely assumed that the early primary contest was a two-handed battle between Mr. Romney and Michael Huckabee, the former Arkansas governor who has seen his popularity soar in recent months.

Mayor Giuliani, who until yesterday led the national polls for more than a year, has opted largely to ignore the early primaries in favor of concentrating on the large states, beginning with Florida on January 29.

As a mark of Mr. McCain’s new confidence, last night he abandoned campaigning in New Hampshire, where he has been making rapid strides in recent weeks, to spend all of today campaigning in Iowa, where until recently even his own aides thought he would fare badly. The early primaries are a game of expectations, with Mr. McCain thought capable of coming in third at best in Iowa and second in New Hampshire.

Better than expected results in either state would add to his new status as the national front-runner, marking a spectacular comeback for the veteran campaigner, providing him with coveted momentum, and winning him much-needed campaign funds.

The national figures from Pew Research released yesterday afternoon show clear evidence of the regained popularity that Mr. McCain’s campaign team has been sensing since the beginning of October.

The polling, conducted between December 19 and 30, shows Mr. McCain at 22%, two points ahead of Mr. Giuliani; with the Iowa front-runner, Mr. Huckabee, at 17%; Mr. Romney at 12%, and Fred Thompson at 9%.

It is Mr. McCain’s best showing in any national poll since May and the first time he has led the Republican pack since January 2007, when a poll for Time magazine briefly put him four points ahead of Mr. Giuliani.

In June and July, Mr. Thompson duked it out with Mr. Giuliani for the top spot before the actor and former Tennessee senator formally entered the race and promptly lost support.

Mr. Thompson has an enormous reserve of funds with which to shrug off early losses, but if he were to drop out of the race before February 5, when 23 states hold their primaries, Mr. McCain could gain many of his supporters.

Mr. McCain’s resurgence coincides with news of the success of General David Petraeus’s troop reinforcements in Iraq, which the senator championed while many of his fellow GOP candidates demurred. The surge in Iraq has spurred a surge in Mr. McCain’s reputation as a patriotic politician with bold proscriptions and sound judgment.

While Mr. McCain’s lead in the national surveys comes as something of a surprise, the latest poll results from New Hampshire are no less startling. Until the end of October, the number of those who said they would back him in the Granite State languished in the upper teens.

Last night the latest poll, by Suffolk Tracking, reflecting opinion December 31–January 1, showed that Mr. McCain had raced ahead of his closest rival, Mr. Romney, with 32% to the former Massachusetts governor’s 23%. Mr. Giuliani attracted 11% support and Mr. Huckabee 10%.

The previous Suffolk Tracking poll, taken between December 27 and 31, showed Mr. McCain easing ahead of Mr. Romney by 31% to 25%.

The New Hampshire figures are a severe blow to Mr. Romney, who has outspent Mr. McCain and all other candidates in the state and who had enjoyed a healthy lead of up to 18% since May.

Two other New Hampshire polls confirmed that Mr. Romney’s hopes of winning New Hampshire easily appear to have been dashed by Mr. McCain’s late dash.

A poll for CNN published yesterday afternoon, conducted between December 27 and 30, showed Messrs. McCain and Romney neck and neck at 29%, with Mr. Giuliani a distant third with 12% and Mr. Huckabee registering 10%.

An American Research Group survey, polled between December 27 and 29, also showed Mr. McCain and Mr. Romney even, at 30%, with Mr. Huckabee at 11% and Mr. Giuliani at 9%.