WASHINGTON —As President Trump put Germany and other allies on notice for the harm they are doing to NATO with their failure to spend adequately on our common defense, Democrats in Washington came to Germany’s defense. “President Trump’s brazen insults and denigration of one of America’s most steadfast allies, Germany, is an embarrassment,” Senate Minority Leader Charles E. Schumer and House Minority Leader Nancy Pelosi said in a joint statement.

Sorry, Trump is right. The real embarrassment is that Germany, one of the wealthiest countries in Europe, spends just 1.24 percent of its gross domestic product on defense — in the bottom half of NATO allies. (The U.S. spends 3.5 percent of GDP on its military.) A study by McKinsey & Co. notes that about 60 percent of Germany’s Eurofighter and Tornado fighter jets and about 80 percent of its Sea Lynx helicopters are unusable. According to Deutsche Welle, a German parliamentary investigation found that “at the end of 2017, no submarines and none of the air force’s 14 large transport planes were available for deployment due to repairs,” and “a Defense Ministry paper revealed German soldiers did not have enough protective vests, winter clothing or tents to adequately take part in a major NATO mission.” Not enough tents?

To meet its promised NATO commitments, Germany needs to spend $28 billion more on defense annually. Apparently Germany can’t come up with the money, but it can send billions of dollars to Russia — the country NATO was created to protect against — for natural gas and support a new pipeline that will make Germany and Eastern European allies even more vulnerable to Moscow.

Sadly, Germany is not alone. Belgium, where NATO is headquartered, spends just 0.9 percent of GDP on defense — and fully one-third of its meager defense budget is spent on pensions. European NATO allies have about 1.8 million troops, but less than a third are deployable and just 6 percent for any sustained period.

When Trump says NATO is “obsolete,” he is correct — literally.

This is not a new problem. I was in the Pentagon on Sept. 11, 2001, and vividly recall how, when it came time to take military action in Afghanistan, only a handful of allies had any useful war-fighting capabilities they could contribute during the critical early stages of Operation Enduring Freedom. At NATO’s 2002 Prague summit, allies pledged to address these deficiencies by spending at least 2 percent of GDP on defense and investing that money in more usable capabilities. Instead, defense investments by European allies declined from 1.9 percent of GDP in 2000-2004 to 1.7 percent five years later, dropping further to 1.4 percent by 2015.

Little surprise that when NATO intervened in Libya a decade after 9/11, The Post reported, “Less than a month into the Libyan conflict, NATO is running short of precision bombs, highlighting the limitations of Britain, France and other European countries in sustaining even a relatively small military action over an extended period of time.” An alliance whose founding purpose is to deter Russian aggression could not sustain a limited bombing campaign against a far weaker adversary.

President Barack Obama called NATO allies “free riders,” and President George W. Bush urged allies to “increase their defense investments,” both to little effect. But when Trump refused to immediately affirm that the United States would meet its Article 5 commitment to defend a NATO ally, NATO allies agreed to boost spending by $12 billion last year. That is a drop in the bucket: McKinsey calculated that allies need to spend $107 billion more each year to meet their commitments. Since polite pressure by his predecessors did not work, Trump is digging in on a harder line: On Thursday he suggested NATO members double their defense spending targets to 4 percent of GDP.

This is not a gift to Russia, as his critics have alleged. The last thing Putin wants is for Trump to succeed in getting NATO to spend more on defense. And if allies are concerned about getting tough with Russia, there is an easy way to do so: invest in the capabilities NATO needs to deter and defend against Russian aggression.

Trump’s hard line also does not signal that he considers NATO irrelevant. If Trump thought NATO was useless, he would not waste his time on it. But if allies don’t invest in real, usable military capabilities, NATO will become irrelevant. An alliance that cannot effectively join the fight when one of its members comes under attack or runs out of munitions in the middle of a military intervention is, by definition, irrelevant.

NATO needs some tough love, and Trump is delivering it. Thanks to him, the alliance will be stronger as a result.

Marc Thiessen is a columnist with The Washington Post. Follow him on Twitter @marcthiessen.