“No Chinese company is an independent company,” Norbert Röttgen, a former government minister from Ms. Merkel’s party, said recently, adding that Huawei’s involvement was “an imminent question of national security.”

Yet one German telecommunication company, Telefonica Deutschland, has announced that it intends to contract Huawei for its 5G development.

European Union rules make it difficult to target individual companies for political reasons. The bloc could impose stringent standards of conduct and openness for 5G contractors that could be used to restrict Huawei but, as yet, has simply let each member country to decide how to proceed.

Distrust toward the Trump administration is also a significant factor, as European policymakers worry that American sanctions on Huawei are simply a bargaining chip in the United States’ broader trade war with China and might be reversed.

“There is a fear that if you take what potentially are quite expensive decisions with regards to 5G because the Americans have told you that they are a security problem, and then President Trump gets a trade deal with China and suddenly Huawei is all O.K. again, then you’ll feel like the earth has moved under your feet,” said Ian Bond, director of foreign policy at the Center for European Reform, a policy group in London.

Years before the advent of 5G, Huawei was establishing a major presence in Europe, where it ranks third in mobile phone sales, behind Samsung and Apple. The company says it has 12,000 employees, and 23 research and development centers in Europe, a way of building favor and familiarity with policymakers.

And it has moved boldly to position itself in Brussels.

Huawei has spent more than $3 million this year on advertising and lobbying, according to its disclosures in the European Union lobbying registry. That is more than the combined spending of its European 5G competitors, Ericsson and Nokia, and far more than its American rival, Qualcomm.