By Kelly M. McFarland By Kelly M. McFarland July 6 at 5:00 AM

President Trumps second foreign trip kicks off today in Warsaw the first leg of a trip that includes the G-20 Summit in Hamburg and a stop in Paris for Bastille Day. The trip comes in the wake of the turmoil from the presidents European trip to the G-7 meeting in May, with the additional drama of the first Trump-Putin bilateral meeting.

But for Trump and for the United States, the Warsaw stop will present a set of modern-day challenges with historical echoes. On the one hand, Trump probably will have his most favorable meetings in Poland. Warsaws right-wing government and anti-immigration stance, among other things, are more in line with his administrations anti-internationalist stance.

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On the other hand, Poland like much of Europe will also be looking for Trump to put European allies at ease, and make a strong U.S. commitment to NATOs Article 5 treaty. Poland, along with the NATO member states bordering Russia, is fearful of Russias recent aggression spreading westward.

Poland and Estonia are two of only five NATO members that meet the target of spending 2 percentof gross domestic producton defense, a commitment NATO members agreed to work toward after the 2014 Wales Summit. Three other nations in the region, Romania, Latvia and Lithuania, are set to join this list by next year.

Article 5 is the glue holding NATO together

What all of these countries want to hear is a firm statement on Article 5 of the NATO treaty which simply stipulates that an attack on one alliance nation is an attack on them all. This is the core of the NATO alliance, and U.S. adherence to Article 5 dominates alliance members calculations, especially in Eastern Europe. AlthoughTrump pledged U.S. adherence to Article 5 during a June news conference with the Romanian president, many in the alliance remain uncertain, given the presidents failure to make a public commitment during his speech to fellow NATO leaders in May.

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Collective defense was the core of the NATO alliances formation and credibility in 1949, and it remains so. As a crucial first step in NATOs creation and a prerequisite as far as the United States was concerned Britain, France, Belgium, the Netherlands and Luxembourg proved that they could come together for collective defense in the 1948 Brussels Treaty. To solidify a credible deterrent to the Soviet Union, the defense pact needed to expand to include the United States.

The biggest hurdle for the Truman administration at the time was overcoming a historical antipathy against alliances to create the first entangling alliance since the 1778 treaty with France. Realizing what was at stake in the growing Cold War, the administration worked across the political aisle to get key Republicans on board, most notably Sen. Arthur Vandenberg (R-Mich). In short, Vandenberg crafted the requisite legislation that would allow the United States to bind itself to the progressive development of regional and other collective self-defense.

As NATO historian Stanley R. Sloan points out, Today, the collective defense commitment still endows the North Atlantic Treaty with special meaning. It is a potential deterrent against would-be enemies of the allies and a source of reassurance should future threats develop.

Historically, Poland could use some reassurance

Poland hasnt had the best of luck controlling its sovereignty over the past two centuries. It was partitioned between regional powers in the late 1700s and gained independence only in 1918. As we know from more recent history, that didnt last long.

The Nazi-Soviet Non-Aggression Pact of August 1939 divided Poland between Hitlers Germany and Stalins Soviet Union. On Sept. 1, 1939, the German invasion of Poland launched World War II. Berlin eventually reneged on the pact and invaded the Soviet Union in the summer of 1941. The Poles, especially Polish Jews, would suffer some of the worst atrocities of the war.

The Soviet Red Armys liberation of Poland in 1945 and the conclusion of World War II didnt give Warsaw much of a break. Stalin sought a sphere of influence in Eastern Europe to act as a buffer between himself and the West, the direction from which Russias adversaries had come twice in the past 30 years. Against American protests, the Soviets installed a Moscow-friendly communist government in Warsaw, ushering in close to 45 years of Soviet dominance. Warsaw would also become the namesake for the pro-Soviet alliance system the Warsaw Pact created in 1955 to become NATOs counterfoil.

NATOs front lines have shifted

During the Cold War, if a hot war between NATO and the Warsaw Pact was going to begin, the chances were it would begin in a divided Berlin. For more than40 years, the two sides stared at one anotheracross dividing lines with names such asCheckpoint Charlie and weathered a major crisis from 1958 to 1961. The Berlin Walls fall in 1989, Germanys unification and the collapse of the Soviet Union in 1991 ended the Cold War and nightmares of Soviet tanks crossing into Western Europe.

In the past 25 years, NATO expanded eastward to include former Warsaw Pact members such asPoland, as well as former Soviet states. As tensions with a resurgent Russia have risen, many of these states worry that, as in Ukraine and Crimea, the Russians will find a pretext to initiate a hybrid war in the region to regain lost influence and control. This is why such a large portion of Russias neighbors in Europe spend at least 2 percent of GDP on defense, or will by 2018.

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As the Monkey Cage has noted, NATO stepped up its involvement in Eastern Europe in response to Russias actions in Ukraine, including Obama administration-ordered troop increases in Poland and other Eastern European nations. Poland and its Baltic neighbors will be looking for Trump to give strong assurances in a major speech he will deliver in Poland. Mediareports after Trumps May speech at NATO headquarters note that it appears the president intentionally removed a sentence reaffirming U.S. adherence to Article 5.

According to national security adviser H.R. McMaster, the president will reiterate Americas commitment to NATOs common defense this week in Poland. Whether this is a formal adherence to Article 5, a common understanding of the threat Russia poses to the region, or continued backing of American forces in the Baltics and Poland remains to be seen.

Kelly M. McFarlandis a U.S. diplomatic historian and director of programs and research at Georgetown Universitys Institute for the Study of Diplomacy and an adjunct professor in the Walsh School of Foreign Service.

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As Trump leaves for Europe, a question looms: Will he really commit to NATO once and for all? - Washington Post