German Foreign Minister Sigmar Gabriel says it's a "decisive period" for US-European relations.

While he's "optimistic" about working with President Trump, "admittedly, many things are irritating us," Gabriel said Tuesday in Berlin.

"We should not only respond to messages or tweets, we should ask what is our role" in proactively shaping policy, said Gabriel at the German-American Conference, a meeting of US and German government and business leaders.

As Germany's top diplomat, Gabriel is emerging as someone willing to stand up to Trump on the world stage. He made headlines recently for calling Ivanka Trump's visit to Germany "nepotism." On Wednesday, Gabriel is set to meet with US Secretary of State Rex Tillerson in Washington DC.

The Trump Administration has made it clear that it thinks Germany should spend a lot more money on its military. Tillerson says Germany can afford to spend at least 2% of its $3.5 trillion GDP on defense. At the moment, Germany spends closer to 1%.

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Gabriel has repeatedly dismissed the 2% goal as neither "reachable nor desirable." But he did say this week that "Europe must develop hard power" if it is going to maintain a top leadership role on the world stage alongside the US and China.

He's also not happy about the Trump Administration's threats to erect trade barriers and to pull out of the Paris Agreement on climate change and the Iran nuclear deal.

"It's in the long-term interest of all of humanity that the US doesn't quit" the Paris Agreement, Gabriel said on the eve of his trip to the US.

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Gabriel believes the biggest challenge today is convincing people outside of the elites that globalization is working.

"We have to bring those parts of our societies in contact that don't meet regularly in the frequent flyer lounge in Frankfurt," Gabriel said at the conference, which was hosted by the Atlantik-Brucke and the American Council on Germany.

A lawyer in Boston has more in common today with a lawyer in London or Berlin than he or she does with a farmer in Iowa, Gabriel argued. He says we can't ignore the farmers.

"This is our challenge if we don't want our relations to erode even more," Gabriel told the crowd in Berlin.