“Americans cannot care more for your children’s security than you do,” U.S. Defense Secretary James Mattis cautioned NATO defense ministers in Brussels in mid-February, urging European allies to get serious about providing for their own defense.

Mattis put the alliance on notice that U.S. patience was finite and suggested that Washington’s commitment to European security was potentially at risk, noting, “[If] your nations do not want to see America moderate its commitment to the alliance, each of your capitals needs to show its support for our common defense.”

Do Mattis’s warnings represent a genuine shift in U.S. policy on European security? Here are three things to know.

1) U.S. concern over European allies’ low levels of spending is not new. Mattis is only the latest U.S. defense secretary to voice frustrations about NATO burden-sharing. Former secretaries Ashton Carter, Leon Panetta and Robert Gates all offered similar concerns during their tenures at the Pentagon. Even former president Barack Obama expressed worries about “free riders” in Europe. This sentiment is not without merit, as the United States is the leading direct funder of NATO — and U.S. defense spending represents nearly 75 percent of the total defense spending of the 28-member alliance.

Washington’s weariness over being Europe’s dominant security provider are long-standing and bipartisan. However, while Mattis was more diplomatic in his choice of language compared with President Donald Trump’s acerbic style, the implication was clear. The U.S. security commitment to Europe depends on alliance partners meeting their 2006 promise to spend 2 percent of GDP on defense.

2) NATO’s target of 2 percent of GDP defense spending obfuscates as much as it reveals. Although Mattis’s statements might compel NATO allies to spend more, this spending will not necessarily produce a better-prepared or more unified alliance. Defense spending is an indirect indicator of military readiness and includes variables that may have only an ancillary effect on military strength — budget entries such as salaries, health care, pensions, accommodations, training and logistics. These noncombat budget items can easily devour defense spending.

Each of the 28 NATO member states have different means and methods of spending. Allies that rely on conscription, such as Norway and Estonia, may be able to spend less on personnel per unit than countries with an all-volunteer military. States with socialized health care, such as Britain, do not have to pay separately for a parallel military health system, such as the one available to the U.S. military and their families.

Defense budgets are also tethered to a country’s relative purchasing power and spending efficiency. States that use military spending for economic development or political purposes can spend more without necessarily improving combat readiness. Valeri Ratchev, a Bulgarian defense expert, perhaps put it best when he wryly suggested that the best way for a country to meet the 2 percent spending target was simply to double the salaries of troops.

“Front-line” states bordering Russia are already spending more. Poland and Estonia spend at least 2 percent of GDP on defense, and other states on NATO’s eastern flank are increasing their budgets in response to Russia’s annexation of Crimea in 2014. Yet Eastern European allies remain the most vulnerable of the NATO states.

By comparison, several of the most militarily credible NATO members don’t quite hit the 2 percent target. France, one of the few NATO states capable of conducting large, complex military operations independently, spends just 1.78 percent of GDP on defense. Turkey, which operates extensively in Syria and fields the second-largest military in NATO after the United States, spends 1.56 percent of its GDP on defense.

Greece is one country that does hit the 2 percent target, spending about 2.4 percent of GDP on defense — despite deep economic difficulties. But the bulk of Greek defense spending is oriented to counter neighboring Turkey, a fellow NATO member.

3) The greater threat to NATO military readiness is about willpower, not money. Divergent threat perceptions and parochial interests among the 28 members do more damage to NATO’s military credibility than spending ratios. As Russia demonstrated in Georgia, Ukraine and Syria, decisiveness and first-mover advantage can compensate for limited resources and sophistication — Russia’s defense budget is barely larger than Britain’s and smaller than Saudi Arabia’s.

Conversely, there is little evidence to suggest that a better-funded army would make more dovish allies such as Germany more inclined to more aggressively confront Russian aggression. While its recent troop deployment to the Baltics sends a strong message, Germany is generally regarded as skeptical over deterring Russia, and even toward NATO obligations overall.

A 2015 Pew survey found that only 38 percent of Germans supported using force to defend NATO allies, compared with 56 percent among U.S. respondents and 53 percent in Canada (which spends less than 1 percent on defense). The relevant measure of Germany’s commitment to collective security is its willingness to act, not whether it spends 1 percent — or 10 percent — on defense.

Threat perceptions diverge strongly throughout the alliance. Even in Afghanistan, many NATO states chose to constrain their involvement through “national caveats.” Troop contingents from Germany, Italy and Spain, for instance, were restricted in the types of operations they conducted in-country, leaving more dangerous missions to contributors without caveats, such as the United States, Britain, Poland and over-performing non-NATO partners such as Georgia.

It is not difficult to understand why the United States would seek more equitable spending from NATO allies, but Washington gains more from the security architecture NATO enshrines than it would from marginal increases in European defense spending. NATO has been a good deal for U.S. national security; its founding helped arrest a spiral of destructive intra-European conflicts and established norms that contributed to an unprecedented period of peace and prosperity in much of North America and Europe.

So even if every NATO ally hit the 2 percent target, Washington would still easily dominate aggregate NATO defense spending. The new administration’s tough talk may make for good politics, but it is unclear whether it will do much to make Europe — or the alliance — stronger.

Michael Hikari Cecire is an international security analyst and a nonresident fellow at New America and the Foreign Policy Research Institute.