Right Now: Protesters are on the streets as world leaders gather in Hamburg, Germany, for the Group of 20 summit meeting.

• Several high-profile issues are on the agenda of the gathering, which gets underway midmorning: climate change, global trade, North Korea, Syria and Ukraine. Leaders will also be meeting in smaller groups.

• The summit meeting will bring together the world’s most powerful leaders, but the focus is likely to be on one particular face-to-face encounter: between President Trump and his Russian counterpart, Vladimir V. Putin. They are expected to meet at 3:45 p.m. local time.

• Mr. Trump was active on Twitter on Friday morning. He described the reaction to his speech in Poland and a meeting with Chancellor Angela Merkel of Germany as “great,” and then said “everyone here” is talking about John Podesta, Hillary Clinton’s campaign manager.

• Mr. Trump wants the United States to wield its economic dominance to dictate the rules of global trade, but other countries seem unwilling to follow. As if to make that point, the European Union and Japan agreed on Thursday to the outlines of a trade deal that would diminish opportunities for American companies.

Protesters get an early start, and the police are there to meet them.

Hamburg awoke to the buzz of helicopters and the wailing of sirens as police officers rushed to keep up with hundreds of protesters who gathered early Friday at major intersections in the city, in an effort to block the routes G-20 leaders were to take to the convention center.

“We remind you that gatherings in the transit corridors will not be tolerated,” the police said on Twitter. Video footage from Hamburg showed the authorities using water cannons to stop the protesters from advancing.

Demonstrations on Thursday night turned violent after the police moved in to separate a group wearing balaclavas and masks — which German law forbids during public protests — in a section of the 12,000 people who filled the streets outside the security perimeter.

Police officers said they had been hit with bottles and stones, and that they had responded with water cannons and pepper spray. Protesters said they had been provoked by officers dressed in riot gear and wielding billy clubs. Seventy-six officers were wounded, and at least five needed to be hospitalized, including a helicopter pilot who had been blinded by a laser. Organizers of the demonstration said “many” participants had been injured, but gave no details. — Melissa Eddy

All eyes on Trump and Putin as they prepare to meet.

The meeting later Friday between Mr. Trump and Mr. Putin is not officially the main event at the G-20, but for many, it might as well be.

Mr. Trump delivered a mixed message on Russia while in Warsaw, issuing his sharpest criticism of Moscow since taking office. He called on Russia to “cease its destabilizing activities in Ukraine,” denounced its support for “hostile regimes,” including Syrian and Iran, and offered unqualified for support for the collective defense principle of NATO (something he was unwilling to do during his first trip to Europe as president in May).

At the same time, he broke with American intelligence agencies by saying he was not entirely convinced that Russia was solely responsible for interference in the 2016 election.

In Moscow, there is the sense that Mr. Putin will be able to outwit and outposition the American leader and come out on top. “It is a win-win situation for Putin,” said Andrei V. Kolesnikov, a political analyst at the Carnegie Moscow Center, though it will not be all clear sailing for Mr. Putin.

The two leaders find themselves on opposite sides of several important issues, including climate change and Western sanctions imposed after the annexation of Crimea. The Kremlin is also rankled by a missile defense system that the United States is building in Eastern Europe.

They might find some common ground on counterterrorism efforts, broadly speaking. But in Syria, Moscow is backing President Bashar al-Assad, while Washington still wants to see him step down.

What’s on everyone’s mind in Germany? It’s John Podesta, Trump says.

On a day in which he might — or might not — confront Mr. Putin on Russia’s attempts to sway the 2016 election, Mr. Trump decided to mount a diversionary attack against an American adversary.

“Everyone here is talking about why John Podesta refused to give the DNC server to the FBI and the CIA. Disgraceful!” Mr. Trump wrote in a tweet sandwiched between polite happy-to-meet tweets about Mr. Putin, Ms. Merkel, and Prime Minister Shinzo Abe of Japan.

Mr. Trump’s tweet was off the mark on three counts:

• Mr. Podesta was Hillary Clinton’s campaign chairman at the time and had no authority to turn over anything, much less someone else’s emails, to the F.B.I. and C.I.A.

• Mr. Podesta — whose own emails were targeted by hackers — fully cooperated with law enforcement agencies.

• The Democratic National Committee, which was leery of the F.B.I. because of its inquiry into Mrs. Clinton’s use of a private email server, did deny investigators access to their servers. But it gave the bureau information that later pointed to Moscow’s interference in the election, according to congressional testimony from James B. Comey, the former F.B.I. director. . — Glenn Thrush

A ‘great’ start to G-20 meetings, Trump says.

Mr. Trump, who is expected to face a tense set of meetings in Hamburg, seemed to have awakened Friday morning pining for his relatively peaceful visit to Warsaw, where a cheering crowd of Polish right-wing party loyalists applauded his speech.

In a tweet Friday morning, Mr. Trump said he had had a “great” meeting Thursday night with Ms. Merkel, with whom he has had a difficult relationship, and whose positions on climate change and liberalized trade clash with his own.

And he said the same of his dinner with Prime Minister Shinzo Abe of Japan and President Moon Jae-in of South Korea, at which the leaders talked privately about responding to North Korea’s latest provocations. — Julie Hirschfeld Davis

To meet with Putin, Trump will have to miss most of a session on climate change.

Mr. Trump’s meeting with Mr. Putin means that will have to cut short a potentially uncomfortable discussion on climate change, a major element of the agenda on which he has broken with European allies.

Their meeting on Friday is scheduled to begin just 15 minutes after the start of a the G-20 working session on “Sustainable Growth, Climate, and Energy,” a discussion in which the president’s decision to withdraw from the Paris climate accord is likely to figure prominently.

If his counterparts plan to lecture or otherwise challenge Mr. Trump on the matter, they will only have 10 minutes in which to do so. Mr. Trump is scheduled to leave early for his sit-down with Mr. Putin. — Julie Hirschfeld Davis