But many security experts have questioned that argument.
“We are just not credible anymore,” said Jan Techau, director of the Europe Program at the German Marshall Fund in Berlin. “First we said 2 percent, but we didn’t really mean it. Then we said 1.5 percent, and it turns out we didn’t really mean that either.”
Defense spending is still on course to increase next year, rising from 1.35 percent of G.D.P. this year to 1.37 percent next year, finance ministry officials said. But by 2023, according to the latest budget figures, it is expected to be back at 1.25 percent.
The latest trans-Atlantic conflict is in part rooted in Germany’s domestic politics.
The finance minister, Olaf Scholz, who drafted the new budget plan, is a member of the Social Democrats, the center-left coalition partner of Ms. Merkel’s Conservatives. Ahead of a string of European and regional elections this year, the Social Democrats, whose poll ratings have plummeted in recent years, are eager to distinguish themselves by giving priority to social spending over defense.
Some political leaders like Michael Grosse-Brömer, the conservative caucus whip, said that Parliament was expected to approve a continuation of its current military missions in Afghanistan, Mali, South Sudan and the Mediterranean, and that Germany still intended to uphold its spending commitments to its NATO partners. But he, too, conceded that “the current plan looks somewhat different.”
One wild card is economic growth, which is set to slow in coming years, making it easier to increase defense spending as a percentage of G.D.P. The German Council of Economic Experts scaled down its growth forecast for the current and coming years to 0.8 percent and 1.7 percent, respectively, saying that “the boom years are over.”
But it is time for Germany to look beyond electoral horizons and consider defense spending in a longer-term, strategic framework, said Ms. Smith, the former Obama adviser.
“Imagine Trump left NATO tomorrow,” she said. “Imagine the investment Germany would have to make in its own and Europe’s security then.”
“This is the cheap version,” she said of the current NATO spending targets.