At NATO’s recent Hague summit, the security allies committed “to invest 5 percent of their GDP annually on core defense requirements as well as defense- and security-related spending by 2035,” a target long pushed by President Donald Trump.

“It’s a monumental win for the United States,” he crowed.

These NATO member commitments are certainly overdue. But how plausible are they?

During the Cold War, French and German defense spending exceeded 3 percent of GDP. So larger military expenditures are not unprecedented. 

But increased defense spending by NATO members can only come from three places: tax revenue, cuts in other government spending or borrowing.

In 1970, when Bonn spent 3 percent on defense, the German economy was growing at 5.1 percent. This year the German economy is not expected to grow at all. The French economy, which was growing by 6.2 percent in 1970, is forecast to expand by 0.6 percent this year. Slower growth means less tax revenue available for defense.

And for a number of NATO members, it is not economically or politically plausible to raise taxes.

Government revenue as a share of the economy was 21 percent of GDP in 1970 in France, when it was growing. It is now 52 percent. In Spain it is 42 percent. In Italy it is 47 percent.

If faster growth and raising taxes may be off the table, more defense spending may have to come from cutting other government expenditures.

In France, social spending equals 32 percent of GDP; in Germany it is 27 percent. The United States spends 29 percent on its social safety net.

So, in principle, if the United States can afford to spend 3.4 percent of its GDP on defense, NATO members should be able to increase defense spending without politically problematic cuts in social spending. As with everything, however, the devil will be in the details.

In Germany, for example, more than a quarter (27 percent) of the government’s budget already goes to paying pensions. And nearly 5 million Germans are slated to retire by 2035, shrinking the tax-paying labor force by 9 percent while growing transfer payments to the elderly.

A poll earlier this year in Germany found no majority support for cutting pensions or any other aspect of social spending.

Facing slow growth in tax revenue and constraints on cutting their social safety net, European NATO members intend to borrow to pay for more defense spending.

The EU will allow member states to increase military outlays without facing disciplinary measures for excessive budget deficits. And the German government has created an exception to its constitutional constraint on deficit spending to enable it to boost defense expenditures. 

In the short run, debt financing may be Europeans’ least onerous option. The share of government spending going to interest payments is currently only 4 percent in France, 6 percent in Spain and 9 percent in Italy, compared with 14 percent in the United States. But deficit financing of more defense spending still has its limits. Government debt as a percent of GDP is already 132 percent in Italy, 98 percent in Spain and 92 percent in France, and now it is only likely to grow.

These economic obstacles to meeting the new NATO defense spending targets already face political headwinds. According to polling by the European Council on Foreign Relations, less than half the public in France (45 percent), Spain (46 percent) and Germany (47 percent) support increased national defense spending. And a majority of Italians (58 percent) actually oppose it.

Some of the greatest public concern about spending too much on defense comes from the most populist right-wing European parties, many of which are anti-American.

A plurality (42 percent) of members of the AFD, Germany’s second-largest party, say they are worried about spending too much on defense at the expense of other public spending. A plurality (43 percent) of the National Rally, France’s main opposition party, hold a similar view. In the years ahead, such sentiments among politically significant segments of the population may hobble major NATO countries’ ability to meet their Hague summit commitments. 

Americans who have long complained about the lack of European defense burden-sharing should be pleased with the new NATO spending targets, but we should not kid ourselves. There is a good reason why the spending target date is a decade away: It is going to be very difficult to achieve.

Bruce Stokes is a nonresident fellow at the German Marshall Fund.