KYIV, Ukraine — Russian tanks were rolling over the border and Kyiv, the Ukrainian capital, was in the grips of fear and panic. Street fighting broke out and a Russian armored column, barreling into the city, advanced to within two miles of the office of President Volodymyr Zelensky.
In those tense first days of the war, almost everyone — Russian President Vladimir V. Putin, military analysts and many Western officials — expected the Ukrainian leadership to fracture. Instead, Mr. Zelensky decided to personally remain in the capital, taking selfies as he traversed Kyiv to reassure his people. And he ordered his senior aides, many Cabinet members and much of his government to also stay put, despite the risks.
It was a crystallizing moment for Mr. Zelensky’s government, ensuring a wide array of agencies kept running efficiently and in sync. Leading politicians put aside the sharp-elbowed infighting that had defined Ukrainian politics for decades and instead created a largely united front that continues today.
No senior officials defected or fled, and the bureaucracy quickly went onto a war footing.
“In the first days of the war, everybody was in shock, and everybody was thinking what to do — stay in Kyiv or evacuate,” said Serhiy Nikiforov, Mr. Zelensky’s spokesman. “The president’s decision was no one goes anywhere. We stay in Kyiv, and we fight. That cemented it.”
To much of the world, Mr. Zelensky is best known for appearing by video link with a daily message of courage and defiance, to rally his people and exhort allies to provide weapons, money and moral support. On Sunday he commanded global attention again in a meeting in Kyiv with two top American officials, Secretary of State Antony J. Blinken and Defense Secretary Lloyd J. Austin III, who pledged more military support and — in a move of symbolic importance — said the United States would move to reopen its embassy in Kyiv.
But Mr. Zelensky’s success so far in defending against the Russian invasion is also rooted in the government’s ability to operate smoothly and take measures to help people cope, such as sweeping deregulation to keep the economy afloat, and to provide essential goods and services.
By loosening rules around transporting cargo, for instance, the government was able to address a dire risk of food shortages in Kyiv, the capital, in the early days of the war. And in March he dropped business taxes to 2 percent — and then only if the owner wanted to pay.
“Pay if you can but if you cannot there are no questions asked,” Mr. Zelensky said at the time.
More contentiously, he combined six television stations that previously competed against one another into one outlet for news. The merger, he said, was necessary for national security, but it frustrated political opponents and free speech advocates.
He has also forged a truce with his primary domestic political opponent, former President Petro O. Poroshenko, with whom he had been feuding right up until the start of the war.