BRUSSELS, Belgium (AFP) — United States allies at the North Atlantic Treaty Organization (NATO) scrambled Wednesday to put a brave face on the return of Donald Trump to the White House amid fears the unpredictable Republican could upend European security and pull the plug on Ukraine support.

Trump sealed a dramatic comeback to power after sweeping to victory in the US presidential election against Democrat Kamala Harris.

NATO chief Mark Rutte — chosen recently in part due to his good relations with Trump — was quick to congratulate the victor and played up the positive impact he could make. “His leadership will again be key to keeping our Alliance strong. I look forward to working with him again to advance peace through strength through NATO,” Rutte said.

But beneath the veneer of calm, there remains deep disquiet about what Trump could do to European security as an aggressive Russia wages war on Ukraine just beyond NATO’s border.

The volatile former reality TV star rattled NATO during the campaign by saying he’d encourage Moscow to “do whatever the hell they want” to members not spending enough on defense.

Senior diplomats at NATO, speaking on condition of anonymity to discuss sensitive issues, sought to put a positive spin on his return for a second term, saying it could push Europe to get serious about protecting itself.

“Why be scared by Trump now? It is going to be rough, but at least he will pump some energy into the whole thing,” one diplomat said.

Trump’s first term in power was a rollercoaster for NATO as the bulldozing president lambasted European allies such as Germany for weak defense spending and reportedly even mulled pulling Washington out.

But officials said that not only did the alliance survive — it actually emerged stronger as Trump and his no-holds-barred style pressured Europe to spend more.