LONDON — When Secretary of State Antony J. Blinken arrives in Ukraine early Thursday, he will encounter an all too familiar scene: a country struggling to defend itself from without and reconstruct itself from within.

It is little changed from the days when Mr. Blinken was a White House staffer in the Obama administration — and a warning that solutions might be years away still.

Mr. Blinken is the first senior Biden administration official to visit Kyiv, and his task when he meets with Ukraine’s president, Volodymyr Zelensky, will be to reassure him of American support against Russia’s ongoing aggression, which flared last month when Moscow built up more than 100,000 troops along Ukraine’s eastern border.

Russia began withdrawing those forces in late April but still has many of them and all their equipment in place. Moscow also continues to back a pro-Russian insurgency in a war in Ukraine’s east that has killed more than 13,000 people, according to the United Nations.

At the same time, Mr. Blinken will also renew American calls for change in Ukraine’s notoriously corrupt political system. That message acquired new urgency after Ukraine’s government last month ousted the head of the country’s national energy company in a move a State Department spokesman condemned as “just the latest example of ignoring best practices and putting Ukraine’s hard-fought economic progress at risk.”

Still, William B. Taylor, Jr., a former top American diplomat in Ukraine, said a firm signal of American support against Russia’s president, Vladimir V. Putin, was the clear priority. “The first and most important topic is Ukraine’s ability to stand up to Mr. Putin,” he said.

Mr. Taylor noted that Russian forces have not entirely withdrawn from Ukraine’s border. “There’s still a whole lot of military capability poised to do bad things,” he said.

Looming over Mr. Blinken’s visit is the resurrection of the political machinations involving Ukraine that led to President Donald J. Trump’s first impeachment trial. Last week, F.B.I. agents raided the home and office of Mr. Trump’s personal lawyer, Rudolph W. Giuliani, seeking evidence related to Mr. Giuliani’s role in the removal of the U.S. ambassador to Ukraine in April 2019.

Although that saga is unlikely to be on the official agenda or to affect U.S. policy, it is a vivid reminder of the power of anti-reform figures in the country. Ukrainian associates of Mr. Giuliani pressed Mr. Giuliani to oust the ambassador, Marie L. Yovanovitch, because they viewed her as a threat to their business interests, American diplomats testified during the impeachment hearings in 2019.

Though Mr. Blinken is no stranger to Ukraine, having visited repeatedly during the Obama years, he will be joined by one of the government’s top experts and strongest defenders of the country, Victoria J. Nuland, who last week was confirmed as the State Department’s under secretary for political affairs, its No. 3 position.

As the department’s top official for Europe and Eurasia in the Obama administration, Ms. Nuland became a loathed figure in the Kremlin over her ardent support for Ukraine’s 2014 revolution. Russian officials bitterly recall how Ms. Nuland passed out food to protesters in Kyiv before they toppled Ukraine’s Russian-backed president, Viktor F. Yanukovych.

Ms. Nuland’s visit with Mr. Blinken comes a few weeks before President Biden is likely to meet with Mr. Putin during a trip to Europe. For now, Mr. Taylor said, that meeting in June serves “a hostage” that may be preventing the Russian leader from sending troops across Ukraine’s border, though analysts remain divided about Mr. Putin’s motives in ordering the buildup. Some believe he may be simply trying to intimidate Mr. Zelensky and put Mr. Biden off balance.

Combat has been taking place within Ukraine for seven years, as government forces battle separatists armed and funded by the Kremlin, and a European-led peace process is deadlocked.

Mr. Biden himself has had extensive experience in Ukraine, having led the Obama administration’s actions there as vice president. On Tuesday, he said his “hope and expectation” was that he will meet with Mr. Putin during his trip to Europe, a meeting at which Ukraine is sure to be a central topic of discussion.

With an eye on Russia’s threats and meddling, Ukrainian officials have said they are eager for more security aid from the Biden administration, but it is far from clear whether that will be forthcoming.

Asked last week whether Mr. Blinken might come bearing such offers, Philip T. Reeker, the State Department’s acting assistant secretary for European and Eurasian Affairs, pointed to $408 million in existing U.S. support, and said only, “I’m sure that will come up in our conversation.” Strong support exists in Congress for increasing that funding, Mr. Taylor noted.

During his visit, Mr. Blinken is expected to try to assess how much confidence to place in Mr. Zelensky, a former comedic actor elected in April 2019 with no political experience.

Just last month, President Volodymyr Zelensky donned a helmet and flak jacket to visit his soldiers in trenches at the front, showing defiance to the Russian military buildup. Praise and warm words of support flowed in from Ukraine’s Western allies.

In a statement, the State Department said Mr. Blinken would “reaffirm unwavering U.S. support for Ukraine’s sovereignty and territorial integrity. But he will also encourage continued progress in Ukraine’s institutional reform agenda, particularly anti-corruption action, with is key to securing Ukraine’s democratic institutions, economic prosperity and Euro-Atlantic future.”

In Kyiv, independent analysts have praised the tough-love policy.

“Biden is an opportunity Ukraine can use or lose,” Sergiy Sydorenko, editor of European Pravda, an online news outlet, said in an interview. “By the look of it, Biden really cares for democracy, and having a democratic Ukraine is vital for developments in the wider region, including Russia. But Biden’s support is not guaranteed.”

Anti-corruption efforts in Ukraine have been a mixed bag.

Earlier in his tenure, Mr. Zelensky’s political party and allies passed a law privatizing former collective farmland, a step toward unwinding corruption schemes in agriculture. He also formed an anti-corruption court, and this year, his government sanctioned oligarchs with ties to Russia.

But for Western donor nations that prop up the Ukrainian budget, a critical aspect of Mr. Zelensky’s presidency has been his relationship with an oligarch, Ihor Kolomoisky, whom Ukraine’s own banking regulators accuse of embezzlement. Mr. Kolomoisky denies the allegations.

In March, the Biden administration sanctioned Mr. Kolomoisky and members of his family, and the U.S. authorities have frozen or seized his commercial real estate assets, including an office tower in Cleveland.

Two years ago, a freshly installed Mr. Zelensky was put through the mangle of American politics. A hangover still lingers.

In a phone call in July 2019, while withholding military aid, President Trump asked him for the “favor” of investigating Mr. Biden, a political adversary, and members of his family. Mr. Trump accused Mr. Biden of wrongdoing when he was vice president in the Obama administration.

Untangling this situation became an early headache for Mr. Zelensky in the first months of his presidency.

With seemingly little choice and his country at war and in need of the military assistance, Mr. Zelensky leaned toward helping in the scheme to discredit Mr. Biden. But Mr. Zelensky’s plans to publicly announce the investigation in September in a CNN interview, something that would have sealed his support for Mr. Trump’s position, never came to fruition. By then, a C.I.A. whistle-blower’s warning about the scheme became public and Mr. Zelensky was spared the need to pick a side.

Mr. Zelensky insisted that he had tried to remain neutral throughout, and his aides note that he never publicly endorsed Mr. Trump’s dirt-digging effort.

They say they see no reason for Mr. Biden to hold a grudge.

Maria Varenikova contributed reporting from Kyiv.