President Donald Trump’s pressure campaign on NATO allies to spend more on their own defense is paying off, U.S. NATO Ambassador Kay Bailey Hutchison said.

“NATO really is making progress, and they are doing it really at President Trump’s insistence,” Hutchinson said on “Fox News Sunday.” “It’s very clear, and he’s been very direct about the Europeans needing to do more for their own security.”

Hutchison, a former Republican senator from Texas, took up her NATO role in August. She spoke ahead of a potentially testy summit of NATO nations to be held in Brussels starting Wednesday.

The U.S. has been seeking an increased commitment by alliance members to increase defense spending. In the past few weeks, Trump has sent sharply worded letters to the leaders of several European countries, including Germany, Italy and Norway, and also to Canada, warning that the U.S. was losing patience.

Related: European Leaders Are ‘Scared To Death’ That Trump Might Withdraw US Troops »

“It will become increasingly difficult to justify to American citizens why some countries continue to fail to meet our shared collective security commitments,” Trump said in a letter addressed to Norwegian Prime Minister Erna Solberg seen by Bloomberg News.

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In 2014, NATO members pledged to spend at least 2 percent of economic output on defense by 2024. Estimated 2017 defense spending as a percentage of GDP was 1.2 percent in Germany, Europe’s biggest economy. Only five NATO members –– the United Kingdom, Estonia, Poland, Greece and the U.S. –– were forecast to have met the 2 percent target in 2017.

Some diplomats fear that Trump will threaten to pull troops out of Europe without more spending on defense, despite U.S. denials. Separately, doubts about Trump’s commitment to European security have pushed EU leaders to boost defense cooperation.

Related: Is Trump Out To Dismantle NATO? »

Although Hutchison said threats by Trump to impose tariffs on European cars haven’t come up in the context of NATO, the president has accused European members of the military alliance of denying U.S. companies fair trade access.

Germany’s defense minister last week rebuffed Trump’s twinning of trade and European defense spending. It was “immature” to link the two topics, Ursula von der Leyen said.

A country’s defense contribution shouldn’t be measured only as a percentage of GDP, but also in terms of troops and hardware, she said in an interview with Bloomberg Television in Berlin. Still, Chancellor Angela Merkel, in a weekly podcast Saturday, said Germany would increase defense spending in its 2019 budget, suggesting that Trump’s complaints are paying off.

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©2018 Bloomberg News.  Distributed by Tribune Content Agency, LLC.

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