A review recently commissioned by the German Parliament has determined that the country could legally finance the British or French nuclear weapons programs in exchange for their protection. The European Union could do the same if it changed its budgeting rules, the study found.

The German assessment comes after months of discussion in Berlin over whether Europe can still rely on American security assurances, which President Trump has called into question. Some have called for considering, as a replacement, a pan-European nuclear umbrella of existing French and British warheads.

The assessment provides a legal framework for such a plan. Britain or France, it finds, could legally base nuclear warheads on German soil.

The document states that “President Trump and his contradictory statements on NATO” have led to fears “that the U.S. could reduce its nuclear commitment” to Europe.

While the review is only an endorsement of the plan’s legality — not a determination to take action — it is the first indication that such an idea has escalated from informal discussion to official policy-making channels.

Few analysts believe that Germany or the European Union is on the verge of pursuing a replacement nuclear umbrella. Most German officials still oppose such a plan, which would face steep public opposition and diplomatic hurdles. Even proponents consider it a last resort.

Nonetheless, analysts say, the review indicates the growing seriousness with which Germany is preparing for the possible loss of the American guarantees that have safeguarded and united European allies since World War II.

“Someone wanted to see whether this could work,” said Ulrich Kuhn, a German nuclear analyst at the Carnegie Endowment for International Peace. “It suggests people consider this a possibility.”

While few are convinced Germany could overcome its taboo against nuclear weapons anytime soon, the existence of the assessment suggests that under pressure from Mr. Trump and growing Russian aggression, the taboo has eroded to an extent.

“The fact that they’re asking the question in itself is pretty important,” said Vipin Narang, a Massachusetts Institute of Technology political scientist who studies nuclear states.

“What’s the line? ‘Amateurs worry about strategy, professionals worry about logistics,’ ” Mr. Narang added, saying that the assessment, by evaluating fine-grain legal questions, “is getting into the logistics” of a European nuclear program. Continue reading.