MANCHESTER, N.H. (Reuters) - Donald Trump served notice on Tuesday to those who have refused to take his 2016 White House campaign seriously: The celebrity real-estate developer and former reality show host is no joke.

While Trump had been expected to win New Hampshire’s nominating contest, he swamped the Republican field by almost 20 points, demonstrating that his passionate, anti-establishment supporters could be relied on to show up and vote when it counts.

“It’s a monumental win for Donald Trump,” said Michael Dennehy, a Republican strategist in Concord, New Hampshire, who is unaffiliated with any campaign. “The message is being sent loud and clear that Republicans want to throw Washington on its head.”

Trump still has a long road ahead. He suffers from high unfavorability ratings and is often an undisciplined candidate who invites controversy with his policies and insults, going so far this week as to repeat an audience member’s assertion that U.S. Senator Ted Cruz was a “pussy.”

Yet after finishing second in the Iowa caucuses last week and now first in New Hampshire, Trump can take solace in the fact that rarely is the ultimate nominee from either party not one of the top two finishers in Iowa or New Hampshire.

Since Iowa began holding the first-in-the-nation caucus in 1976, no Republican has finished second there and first in New Hampshire and failed to win the nomination. The two states are the first of the state-by-state nominating contests for the Nov. 8 election to succeed Democratic President Barack Obama.

In New Hampshire, Trump, at least for the moment, put to rest questions over whether his strong showing in polls was illusory, after he underperformed them last week in Iowa.

His immediate prospects were further helped by the failure of any of the establishment candidates to emerge as a clear challenger. Taken together, the mainstream candidates pulled in enough votes to overcome Trump. But no single one came close to him and there are few signs of a major consolidation anytime soon.

“The victory by Trump here has the makings of a major disaster for the establishment,” said Ford O’Connell, a Republican strategist.

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KEY RIVAL STUMBLES

The candidate who had been widely viewed as Trump’s biggest threat, U.S. Senator Marco Rubio of Florida, suffered deep wounds in New Hampshire after a strong showing in Iowa that some pundits believed would propel him to the top ranks of the establishment Republicans.

After stumbling badly in a debate on Saturday, the man who had been considered by many in the party as its best hope to retake the White House finished deep in the middle of the pack.

“Rubio’s disastrous showing shifted the landscape of the entire campaign,” Dennehy said. He added he had conversations with many undecided voters in recent days who liked Rubio but changed their support to other candidates after the debate.

The Republican nomination race now bends southward, with a primary in South Carolina on Feb. 20 the next test. Trump has held a double-digit lead there for months.

After South Carolina comes Nevada, and then a spate of Southern states on March 1. All provide Trump with the chance to consolidate his support before any other candidate amasses enough delegates to pose a real threat.

His toughest opponent in those states will likely be Cruz, the Texas lawmaker who won in Iowa and whose insurgent candidacy is equally worrisome to the Republican establishment.

But Trump appeared in New Hampshire to learn from some of the mistakes his campaign made in Iowa. In recent days, he combined the large-scale rallies for which he has become known with more intimate affairs, an apparent effort to address criticism he was not devoting enough focus to retail campaigning.

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Trump also returned to the populist themes that have characterized his campaign and made him an atypical front-runner for the Republican nomination.

He ripped U.S. corporations for sending jobs overseas and repeatedly slammed the pharmaceutical industry for charging high prices on prescription drugs and the health insurance industry for consistently hiking rates.

His campaign showed more of an ability to reach voters who may not have otherwise engaged in the political process.

Typical were Marjorie Callicutt, 64, and her husband, Fred, 74, who attended a Trump event in tiny Plymouth, New Hampshire, on Sunday. The couple said they would not have been there if the Trump campaign had not called them the day before to tell them about the rally.

Both said they had been persuaded to vote for him.

“He woke up the country,” Fred Callicutt said. “He says things that nobody wants to talk about.”