WASHINGTON — President Trump will learn this week whether he gets a second chance to make a first impression as he returns to Europe and has his first encounter with Russia’s Vladimir Putin.

Trump’s first visit to the continent in May stirred anxieties among his European allies when he declined to endorse NATO’s common defense treaty explicitly and scolded world leaders for not spending more on their armed forces. This time, Trump will use stops in Poland and Germany to try to pull off the tricky balancing act of improving ties with Moscow at a time of particularly fraught relations while also presenting the U.S. as a check against Russian aggression.

In what may be the most-watched event of the four-day trip, the president will meet Putin on the sidelines of an international summit meeting in Hamburg, Germany. Every aspect of the meeting between the two unpredictable leaders is sure to be closely scrutinized as investigations press on into alleged Moscow meddling in the 2016 election and potential Trump campaign collusion.

With those investigations hanging heavy in the air, there is little expectation that the meeting will produce significant progress on difficult issues such as the crisis in Ukraine or the conflict in Syria.

“I can’t imagine any issue they can actually make major headway on, given the poison that surrounds the relationship,” said Michael O’Hanlon, a senior fellow in foreign policy at the Brookings Institution, who suggested it might lay the groundwork for future cooperation.

The Trump-Putin encounter will be one of at least nine meetings the U.S. president will have with foreign leaders while in Hamburg for a Group of 20 summit of industrialized nations.

But first Trump will stop in Poland, where leaders are looking for reassurance that the presence of U.S. and NATO troops there will continue as long as the region’s security is threatened by a resurgent Russia. In return, Trump will be expecting a warm reception as he pays homage to Polish resolve with a speech in Krasinski Square, his first major outdoor address in a foreign country.

Poland’s leaders are closely aligned with Trump’s worldview, and ruling party lawmakers and pro-government activists plan to bus in groups to help ensure an enthusiastic crowd for Trump after his rather awkward European debut in May.

Previewing the trip, White House officials said Trump would reiterate the U.S. commitment to NATO’s Article 5, which says an attack on one member is an attack on all – something he didn’t do at NATO headquarters in Brussels during his first overseas trip but eventually endorsed last month. The president is also expected to cite the need to develop “a common approach to Russia,” his advisers said.

“He’d like the United States and the entire West to develop a more constructive relationship with Russia,” said the White House national security adviser, H.R. McMaster. “But he’s also made clear that we will do what is necessary to confront Russia’s destabilizing behavior.”