Trump sparked fierce criticism from Western officials for suggesting he would not protect countries that failed to meet the transatlantic military alliance's defence spending targets, and would even encourage Russia to attack them.

At the weekend, the comments by the frontrunner for the Republican presidential nomination hung over the Munich Security Conference, a big annual gathering of politicians, soldiers and diplomats that is often a barometer of U.S.-European relations.

European leaders are anxious not only about NATO's future if Trump beats incumbent President Joe Biden in November but also about a hold-up to a $60 billion Ukraine aid package in the U.S. Congress, as Republicans demand border security measures to pass the bill.

Ukrainian and Western leaders say the package is vital as Kyiv's forces struggle almost two years after Russia's invasion began. Moscow said on Sunday it had taken full control of the devastated eastern Ukrainian town of Avdiivka.

European leaders are reaching out to U.S. lawmakers, business leaders and think tanks as part of efforts to influence the Trump camp that began even before his controversial comments a week ago.

Among their arguments: Europe is spending more on defence and will do more; such spending and aid for Ukraine are worth billions to U.S. arms firms; and protecting Europe projects U.S. strength to China - a major focus of Trump's foreign policy.

"We Europeans must take much greater care of our own security, now and in the future," German Chancellor Olaf Scholz told the conference in the luxury Bayerischer Hof hotel, attended by dozens of U.S. lawmakers.

"The willingness to do so is very great," he declared.

OWN INTERESTS

Scholz and other European leaders, such as Dutch Prime Minister Mark Rutte - the favourite to be NATO's next boss - insisted they were getting more serious about defence because it was in their own interests, not because of Trump.

But they aim to persuade Trump and his followers that sticking with NATO, as he did during his presidency despite complaining loudly, would be good for them too.

"It is in the U.S. interest to have a NATO alliance with strong allies that can reinforce U.S. influence," Norwegian Prime Minister Jonas Gahr Stoere told Reuters in Munich.

Late last month, current NATO Secretary General Jens Stoltenberg travelled to the U.S. for a visit partly designed to sell the alliance and support for Ukraine to the Trump camp.

He spoke at the Heritage Foundation, a Trump-friendly think tank in Washington, and visited a Lockheed Martin plant in Alabama that makes Javelin anti-tank missiles.

"The money which is allocated to Ukraine, very much of that money ends up in the United States. Because they buy weapons - for example, the Javelins - from defence producers in the United States," Stoltenberg said in Munich.

Citing U.S concerns about China, he said: "The United States represents 25% of the world's GDP. Together with NATO allies, we represent 50% of the world's GDP and 50% of the world's military might. So as long as we stand together, we are safe."

European leaders say their higher defence spending reflects a view that Russia now poses a far greater security threat.

It also reflects a growing view among European governments that they will have to take more responsibility for their security in the years ahead, regardless of who wins the next U.S. presidential election.

"The U.S. over time, I think, will be less inclined to feel that they have to fully underwrite European security," Latvian Foreign Minister Krisjanis Karins told Reuters.

Eighteen of NATO's 31 members are expected to meet its defence spending target of at least 2% of GDP this year, up from 11 in 2023, the alliance says. Germany and France, the European Union's biggest economies, are among those expecting to reach the goal.

The U.S. spent around 3.5% of its GDP on defence in 2023, according to NATO estimates.

COLD SHOWER

But defence is about much more than spending figures. The U.S. also brings the might of a superpower, its nuclear arsenal, and a U.S.-led command structure to NATO's defence of Europe.

How much impact the Europeans' arguments will have on Trump and Republican lawmakers is an open question.

U.S. Republican Senator J.D. Vance of Ohio - a prominent Trump backer - delivered something of a cold shower to the Munich audience.

He said Russian President Vladimir Putin did not pose an existential threat to Europe, and Americans and Europeans could not provide enough munitions to defeat Russia in Ukraine.

"There are a lot of bad guys all over the world. And I'm much more interested in some of the problems in East Asia right now than I am in Europe," Vance said.

He welcomed increased European defence spending and said he did not expect Trump to pull out of NATO if he returns to the White House. But he said Washington would pivot further to focus on Asia so Europe would have to be much more militarily capable.

"It's not just about money spent - how many mechanized brigades could Germany field tomorrow? Maybe one?" he asked.

"The American security blanket has allowed European security to atrophy."

(Additional reporting by John Irish and Andreas Rinke; Editing by Andrew Cawthorne)

By Andrew Gray