But concerns over the direction of U.S. leadership has made even Washington's strongest partners in Europe reticent to deploy more troops to these hot spots. This lack of trust — combined with the fact that many allies already have significant security commitments of their own — will likely leave the United States with little choice but to make do with the allied support it has in order to finish out its duties in the Middle East.

Western Europe: Able But Unwilling

In Europe, the United Kingdom and France are the two most powerful and strategically important U.S. allies. Both countries have been actively involved in the U.S.-led mission against the Islamic State. The United Kingdom, in particular, has been a major contributor of troops to the U.S. mission in Afghanistan and has almost doubled its forces in the country over the past year at the request of the United States.

France, on the other hand, withdrew its combat troops from Afghanistan in late 2012. But Paris has remained active in operations throughout sub-Saharan Africa, oftentimes alongside U.S. forces. In a May operation, two members of the French special operations forces died freeing an American hostage in northern Burkina Faso. And in October 2017, French forces came to the rescue of U.S. troops who were ambushed in Niger. These contributions notwithstanding, the United States has struggled to mobilize London and Paris in many of the areas in which Washington has sought further allied reinforcements — namely, in Syria and the Persian Gulf.

Ever since Trump unexpectedly announced plans to withdraw U.S. troops from Syria in April, the White House has tried to petition its allies to increase their presence in the country to ease the transition. However, the United Kingdom and France — and all U.S. allies, for that matter — hesitate to maintain forces in Syria absent a U.S. presence for fear of being left without support in a theater in which their troops could easily come into contact with Russian, Turkish and Iranian forces. As a small concession, Paris and Berlin recently pledged to increase their troop contributions in Syria by 10 percent. But this, of course, is still far from the commitment Trump needs to fulfill his pledge to withdraw all U.S. forces from the country.

A similar story applies to the Persian Gulf. Following a series of Iranian-linked attacks on oil transport ships in July, Washington has attempted to marshal a coalition of regional and global allies to better secure tanker traffic and act as a deterrent against future Iranian aggression in the region. However, ever since Trump decided last year to abandon the 2015 Iran nuclear deal — known as the Joint Comprehensive Plan of Action (JCPOA) — most of Washington's global partners have been highly skeptical of its approach to Tehran. And as a result, even the strongest U.S. allies have resisted supporting Washington's proposed security and surveillance initiative in the Persian Gulf, known as the Sentinel program, for fear of being dragged into a full-blown conflict with Iran.

The United Kingdom, however, has been more directly implicated in the Iranian tanker tensions in the Persian Gulf, with Tehran seizing a U.K. vessel on July 20 in response to London's earlier seizure of an Iranian tanker in the Strait of Gibraltar. And thus, unlike other countries, London has openly recognized the need for a naval escort task force in the region. But instead of supporting the U.S. Sentinel program, the United Kingdom initially sought to launch a Persian Gulf security and surveillance initiative of its own, which has so far earned the tentative backing of France, Italy and Denmark. But this began to change following the recent appointment of U.K. Prime Minister Boris Johnson, who has a closer relationship with Trump and whose administration is realizing the limits of implementing a security program in the Persian Gulf without U.S. support.

In addition to France and the United Kingdom, Germany, too, has long been a loyal U.S. military partner. The country, home to Europe's largest economy, currently provides excellent military facilities for U.S. troops and contributes the second-largest contingent of troops in Afghanistan (after the United States). But like its European peers, Berlin also remains concerned over the direction of U.S. leadership in the Middle East. And this, combined with limited public support for significant military engagements abroad, is why Germany was quick to turn down U.S. requests to send troops to Syria or to join with the Sentinel operation in the Persian Gulf.

Eastern Europe: Willing But Unable

A number of other, smaller European countries — namely Poland, Estonia, Latvia, Lithuania and Georgia — remain much more willing to contribute to U.S. military efforts around the world. These countries are, by no coincidence, particularly concerned over the threat of a potential clash with Russia. And thus, they do their best with what resources they have to help the United States in its missions abroad, with the expectation that Washington would return the favor should they ever need help against Moscow. But unlike France, Germany and the United Kingdom, the problem these countries face is not one of reticence, but of capacity.