By Karoun Demirjian July 6 at 1:08 PM

A T-shirt at a souvenir shop in St. Petersburg depicts President Trump and Russian President Vladimir Putin. (Mladen Antonov/AFP/Getty Images)

On the eve of President Trump’s first face-to-face meeting with Russian President Vladi­mir Putin, congressional Democrats are imploring him to raise the subject of Russian meddling in U.S. elections as they excoriate him for not representing the United States’ interests over his own.

“Not raising this [election meddling] matter with President Putin would be a severe dereliction of the duty of the office to which you were elected,” Senate Democratic leaders wrote in a letter sent to Trump on Thursday ahead of the president’s planned meeting with Putin on the sidelines of the Group of 20 conference in Germany. They stressed that it is “critical that you set the agenda from the start and make absolutely clear that Russian interference in our democracy will in no way be tolerated.

“President Putin must understand this can never happen again,” they wrote.

The president’s meeting with Putin on Friday is a high-stakes test for Trump, coming barely six months into his presidency and at a time when various congressional and federal probes into allegations of Russian meddling in the 2016 U.S. presidential elections are kicking into higher gear. To date, Trump has been unwilling to endorse the findings of the intelligence community, which are that Russia — and Putin specifically — ordered a campaign of hacking and dissemination of false information as a means of tilting the political balance toward a Trump victory.

During a news conference in Poland on Thursday, Trump told reporters that the culprit behind the election meddling “could very well have been Russia” or “could well have been other countries,” stressing that “nobody really knows for sure.” He then blamed the Obama administration for not doing more about hacking evidence they had been made aware of in the months before the election.

In a formal speech Thursday, Trump criticized Russia for its “destabilizing activities in Ukraine and elsewhere” and its “support for hostile regimes, including Syria and Iran” — but no mention was made of Russian election meddling, in the United States or in Europe, where similar campaigns have affected France, Germany and other nations.

In a statement, Rep. Adam B. Schiff (Calif.), ranking Democrat of the House Intelligence Committee, charged that Trump’s comments “continue to directly undermine U.S. interests.”

“This is not putting America first, but continuing to propagate his own personal fiction at the country’s expense,” Schiff said. He added that if Trump did not challenge Putin over Russian election meddling, “the Kremlin will conclude he is too weak to stand up to them . . . a historic mistake, with damaging implications for our foreign policy for years to come.”

Trump’s meeting with Putin was upgraded in recent days from an informal huddle to a more formal, sit-down talk. But the president, a self-described political neophyte, will be facing off with one of the most experienced and formidable heads of state on the world stage — and while Trump has eschewed a public agenda for the meeting, Putin is coming in knowing exactly what he wants.

At the top of the Russian president’s list is securing a promise from Trump that the United States will hand back control over two compounds that were seized from Russia in late December, when the Obama administration accused Moscow of using the facilities for intelligence-gathering purposes and kicked out 35 Russian operatives. If Putin insists upon that during his meeting with Trump, it could force the issue of Russian election meddling out into the open, as the Obama administration took those measures in response to Russia’s alleged hacking and disinformation campaign. But the Trump administration has already been considering returning those compounds.

Lawmakers in the Senate and several in the House had hoped to avoid a scenario where the president could make concessions to the Russian president during their meeting by passing a bill that would step up sanctions against Russia and gives Congress the power to stop any change in sanctions policy — such as handing compounds back to Russia — before the president can effect it. The legislation has overwhelming support, passing the Senate by a vote of 98 to 2, but stalled at the threshold of the House over a technical violation, and House leaders have not yet committed to putting it on the floor.

That bill would cover sanctions related to Syria and Ukraine in addition to punitive measures for Russia’s alleged election meddling.

While the president’s team has shown more willingness to take on Russia over its support for separatists in Ukraine and Syrian President Bashar al-Assad, it is unclear exactly how Trump will broach those topics with Putin. Secretary of State Rex Tillerson recently expressed openness to talk about a Ukraine peace deal outside the confines of the Minsk accords, the agreed-upon peace process and the pathway the Obama administration defined for lifting Ukraine-related sanctions against Russia. And in Syria, the Russians shut down the deconfliction channel after Trump ordered a strike against a Syrian airfield following a sarin gas attack on civilians.

Coordination with Russia in Syria is becoming increasingly urgent as forces make gains on the Islamic State strongholds of Mosul in Iraq and Raqqa in Syria: Once their common enemy, the Islamic State, is gone, the United States and Russia might be thrown into an increasingly direct confrontation, as their allies shift to battling over who will control the newly liberated areas.

Putin will probably also pressure Trump to back a plan for North Korea that would limit the U.S.’s ability to conduct military drills and exercises in conjunction with South Korea in exchange for reining in Pyongyang’s ballistic missile program. That approach runs counter to the approach the Trump administration embraced this week, when the United States and South Korea responded to North Korea’s first-ever test of an intercontinental ballistic missile by conducting a missile drill as a show of force.