WASHINGTON (Reuters) - Donald Trump is facing bipartisan pressure to adopt a more presidential tone in his White House run including from Democratic President Barack Obama and Republicans who worry his missteps may do irreparable harm to the party and his campaign.

The Republican front-runner came under fire from Obama on Friday over Trump’s recent comments that he would not rule out using nuclear weapons in Europe and that Japan and South Korea might need nuclear weapons to ease the U.S. financial commitment to their security.

“The person who made the statements doesn’t know much about foreign policy or nuclear policy or the Korean peninsula, or the world generally,” Obama told a news conference at the conclusion of a nuclear security summit in Washington.

“I’ve said before that people pay attention to American elections. What we do is really important to the rest of the world,” he said.

Trump lost ground on the online prediction market after drawing fire for his suggestion earlier in the week, which he later dialed back, that women be punished for getting abortions if the procedure is banned.

Those who marveled at Trump’s rise are now warning the New York billionaire that his shoot-from-the-lip approach to campaigning could jeopardize his chance to win the Republican nomination for the Nov. 8 election.

Tuesday could be a turning point when Wisconsin hosts its nominating contest. Trump, 69, trails his leading rival, U.S. Senator Ted Cruz, 45, of Texas in the Upper Midwestern state.

A Cruz win would make it harder for Trump to reach the magic number of 1,237 delegates needed to secure the nomination before the Republican national convention in July. The winner will get to claim all of Wisconsin’s 42 delegates.

“If he continues to fumble the ball, he risks everything,” said David Bossie, who as president of the conservative group Citizens United has helped to introduce Trump to grassroots activists. “These types of ham-handed mistakes give his opponents even greater opportunity.”

But losing the Republican nomination may not keep Trump out of the November election.

In excerpts of an interview on “Fox News Sunday” to be aired this Sunday, Trump said he wanted to run as a Republican but declined to rule out a third-party candidacy.

U.S. Republican presidential candidate Donald Trump waves to onlookers and reporters as he departs through a back door after meetings at Republican National Committee (RNC) headquarters in Washington March 31, 2016. REUTERS/Jonathan Ernst

Asked what he would do if he didn’t get the Republican nomination, Trump replied: “We’re going to have to see how I was treated.”

TRUMP, PARTY TALK UNITY

A businessman and former reality TV show host, Trump has never held public office but hails his mastery of negotiating business deals as the sort of experience a U.S. president needs to be successful at home and abroad.

He sent ripples through the Republican Party, which promotes a muscular foreign policy, by declaring NATO obsolete and for asserting that as president he might loosen the ties with longstanding U.S. allies.

Trump made a surprise visit on Thursday to the Republican National Committee in Washington where he said he and Chairman Reince Priebus discussed how to unify the party going into the July convention.

Priebus also addressed any confusion Trump may have had about delegate allocation rules that will govern the proceedings, a source familiar with the meeting told Reuters.

Should Trump fail to win enough delegates to secure the nomination outright in the state-by-state contests ending in June, party delegates will select a nominee at the convention in a complex process of sequential votes.

Online predictions market PredictIt said on Friday that the probability Trump will win his party’s nomination has dropped sharply in the past week while the likelihood of a contested convention to choose another candidate has risen.

CAMPAIGN STYLE A RISK

Those Republicans who see in Trump a chance to generate voter turnout beyond party regulars to blue-collar Democrats and win the White House say his detail-free style of campaigning has come back to haunt him and he needs to gear up for a new phase.

Trump needs to be less sensitive about attacks from opponents and let some go by without responding, said retired neurosurgeon Ben Carson, a former Republican presidential candidate who dropped out of the race earlier this year and has since endorsed Trump.

“If he can just get beyond that and learn how to bite his tongue and redirect people to something that is important, it will show a level of statesmanship,” Carson said.

During the Wisconsin campaign, Trump has relentlessly attacked the state’s governor, Scott Walker, another Republican who dropped out of the presidential race last year and who has endorsed Cruz.

Former U.S. House of Representatives Speaker Newt Gingrich, who has offered Trump informal advice, said Trump should replicate the type of performance he gave at the American Israel Public Affairs Committee on March 21, when he spoke from a teleprompter and offered a well-thought-out case for strong U.S.-Israeli relations.

Gingrich said Trump should make eight to 10 policy speeches in order to give voters “a sense of stability and seriousness.”

“He’s gone from being an insurgent that people laughed at and a front-runner that people were amazed by to the potential nominee. That requires you to change your role as all this comes together,” Gingrich said.

Alternatively, Trump could start to listen to what he says is his wife Melania’s longtime admonishment: “Darling, be more presidential.”

Former Secretary of State Hillary Clinton and U.S. Senator Bernie Sanders will compete in Wisconsin on Tuesday on the Democratic Party side. Both have hop-scotched between Wisconsin and New York, which holds its primary on April 19.

Clinton, a former U.S. senator from New York with national campaign headquarters in Brooklyn, is trying to prevent the Brooklyn-born Sanders, who represents Vermont in the Senate, from eroding support on her home turf. Both candidates will attend a state party fundraising dinner in Wisconsin on Saturday.