President Trump was right to send letters to American NATO allies requesting that they increase defense spending. First reported on by the New York Times, the letters have caused concern in European circles and among the foreign policy establishment in the U.S.

Speaking to the New York Times, a Democratic Party defense official, Derek Chollet, claims the letters are poorly timed in the run up to next week's NATO summit. That's because, Chollet says, "[The Europeans] are hoping to survive [the summit] without irreparable damage, and so the fact that you have all these storm clouds surrounding NATO and Trump is really worrisome."

I disagree. I believe the letters are perfectly timed.

The central issue here is whether Trump's letters make NATO stronger or weaker. I believe Trump strengthens the alliance with this prod. While it's true that Russian President Vladimir Putin's overriding strategic objective is degrading NATO's credibility, and thus that Trump's feuding with European leaders sparks smiles in the Kremlin, Trump's approach here will win dividends at the margin of where it matters.

The British and French governments are boosting their defense spending, and other states like Poland and the Baltics are following suit. The U.K. is likely to announce further spending boosts in the coming months. Although not the only reason for these spending developments, Trump's complaints help a lot. And the spending boosts mean more capability to defeat any external or internal attack on NATO interests.

The problem is that some nations are continuing to starve their militaries and to ignore Trump in the hope that he'll shut up.

Canada and Germany continue to deny the military the resources they need simply to operate their current arsenals, let alone to buy and operate new defense platforms. Belgium, which has the honor of hosting NATO headquarters but spends a pathetic 0.90 percent-of-GDP on defense (2.0 percent is the NATO benchmark), is particularly shameful. Responding to Trump's letters, Belgian Prime Minister Charles Michel told reporters last week, "I am not very impressed by this type of letter. Belgium has halted the systematic fall in defense spending and takes part in a lot of military operations."

Michel's comments speak perfectly to why Trump is right to send aggressive letters.

While Michel talks a good faux-outrage game, the latest NATO defense spending figures show that Belgium is the second lowest percentage-of-GDP defense spender in NATO. Belgium is also the NATO member which spends the second lowest proportion of its defense budget on equipment, which matters as a measure of strike capability.

Then, there's Europe's largest economy, Germany, which is boosting defense spending but at snail-like speed from a low level. NATO analysts estimate that Germany spent just 1.24 percent of GDP on defense in 2017. Simultaneously, and under Trump's pressure to do otherwise, Germany continues to lead the European Union in its deference to Russian energy blackmail.

These realities do far more damage to NATO's credibility than do Trump's barbs. But the dynamic is not going to change unless Trump is relentless with the Europeans, cajoling them to act in support of their common defense and challenging them where they pretend to be doing as much as they can.

Still, the greatest argument in Trump's favor here is the functional action of American power in NATO. Because while Trump's detractors claim that he is undercutting the U.S.-led international order and weakening NATO, reality says differently. Reality points to escalating U.S. military forward deployments to NATO states on the Russian periphery and the boosted means to defeat Russian forces in the event of war. These tangible actions must always be considered in the context of Trump's tweets.

So yes, Trump is right to write these letters. And if things continue without change, the president should relocate U.S. military forces in Europe to the bases of more reliable allies and reemphasize a forward-reaching U.S. military posture that degrades the opportunities that Russian war strategy endeavors to exploit.