I traveled to Eastern Europe last week with a small, bipartisan group of senators to meet with the leaders of Ukraine, Lithuania and Georgia. These former Soviet republics have become reliable U.S. allies as their citizens have sought a democratic future with greater freedom and prosperity. But they need our help.

What I found most troubling on this trip was the renewed Russian effort to destabilize these young democracies. Each is facing increasing pressure from Russia, including military threats on their borders, cyberattacks and political disinformation campaigns. In Ukraine and Georgia, Russia continues to occupy and militarize territory it annexed illegally.

The U.S. must continue to stand with democracies under threat and opposed to Russia’s tyranny. When President Biden meets with Russian President Vladimir Putin in Geneva later this month, he must take a strong stand for freedom, democracy and human rights. The free world will be watching.

Specifically, Mr. Biden must raise the May 23 hijacking of a passenger airliner by Belarusian security forces. In a clear violation of international law, Belarusian President Alexander Lukashenko, an economic client of Mr. Putin’s, ordered his fighter jets to ground the plane forcibly so police could seize Roman Protasevich, a prominent Belarusian journalist and critic of the government, and his girlfriend, Sofia Sapega.

This was no isolated incident for Mr. Lukashenko, who was fraudulently re-elected last August to his sixth term as president. In March, the State Department released a human-rights report calling Belarus “an authoritarian state.” Its list of human-rights abuses committed in the wake of the election included “unlawful or arbitrary killings as well as torture” and “widespread use of brute force against and detentions of peaceful protestors.”

Mr. Biden should continue to call for the immediate release of Mr. Protasevich and Ms. Sapega, make clear that their detention is illegal and immoral and voice strong support for Belarusian opposition leader Svetlana Tikhanovskaya, who stands opposed to autocratic rule. I had the privilege of meeting this courageous leader in Lithuania and I admire her unwavering commitment to democracy for Belarus. Mr. Putin has it in his power to denounce Mr. Lukashenko’s actions and remove all Russian troops from Belarus.

Words from U.S. leaders are important but not enough. Mr. Biden should impose sectoral sanctions targeted at the Lukashenko regime. I called for this when I was in the region last week because it would send the signal that America means what it says.

At the coming summit the president must also confront Mr. Putin over Ukraine. Russia’s latest buildup of military forces in Crimea and Donbas is illegal, and despite Mr. Putin’s claims to the contrary, the great majority of Russian-aligned forces remain in the region. It is in Russia’s interest to see Ukraine struggle, so Mr. Putin will stay the course until America and its allies push back in Ukraine’s defense.

The Trump administration took bold steps to assist Ukraine against Russian aggression, including America’s first-ever sale of lethal arms to Ukraine, so it could defend itself. As co-chairman of the Ukraine Caucus, I have worked to ensure the Senate has provided more-robust security assistance every year–on a bipartisan basis–to this vital ally.

The best way for Mr. Biden to help Ukraine now is to reverse his decision to waive the congressionally mandated sanctions against Russia’s Nord Stream 2 pipeline project. The pipeline runs under the Baltic Sea, bypassing Ukraine. It would increase Europe’s dependence on Russian gas supplies and hurt Ukraine by depriving it of billions of dollars in transit fees. Secretary of State Antony Blinken said in March that the administration believed the pipeline was “a bad idea.”

Ukraine has its own work to do in enacting economic and judicial reforms. The state must continue to build trust with citizens by increasing transparency and developing a system of checks and balances. In my meeting with Ukrainian President Volodymyr Zelensky, we talked about strengthening democracy and rooting out corruption as well as Ukraine’s goal of joining the North Atlantic Treaty Organization. The Biden administration should support this to signal that the U.S. and Europe are serious about standing up for our friends in the region and against Russian belligerence.

Finally, while in Georgia, I visited the administrative boundary line with South Ossetia and witnessed firsthand Russia’s occupation of Georgian territory and its continued “borderization” efforts to legitimize an illegal annexation.

Georgia is one of America’s closest allies in the region, so Russia’s actions should be concerning. While meeting with Georgian Prime Minister Irakli Garibashvili and other leaders, including from opposition parties, we emphasized the need to collaborate to implement the electoral, judicial and economic reforms necessary for a more secure future.

As with Ukraine, the Biden administration should urge NATO to provide a Membership Action Plan for Georgia and help fulfill the promise made at the 2008 Bucharest Summit.

There is bipartisan support in Congress for those in Eastern Europe fighting for a democratic future, but Russia will continue to place obstacles in the way. Mr. Biden should address this forcefully at the summit. Strong American leadership will unite the free world in pushing back against Russia’s malign behavior.

Rob Portman, a Republican, is the junior senator from Ohio and hails from the Cincinnati area.