The government has opened a new investigation and hauled up political enemies for questioning — even as his party is tightening its grip on the judiciary. His critics say he is using Smolensk as a pretense to arrest political enemies before elections in 2020. Others wonder if he is simply gripped by anguish, vengeance and paranoia, and is dragging his country along with him.

Or, perhaps, it is both.

“It is impossible to overestimate the significance of the Smolensk crash in the life of Jaroslaw Kaczynski — and in the life of Polish politics in general,” said Marek Migalski, who ran for the European Parliament as a Law and Justice candidate in 2010 and is now a lecturer at the University of Silesia in Katowice. “For Kaczynski,” he added, “public debate is no longer a political one — between people of different values; it’s an eschatological war between good and evil.”

For years, Mr. Kaczynski’s party has pointed to a host of possible devious scenarios — a thermobaric bomb that blew up the plane without leaving evidence; assassins using artificial fog to obscure the runway. But the heart of the narrative boils down to two basic unproven accusations: The Russians did it, and Polish political opponents of Mr. Kaczynski deliberately conducted an inadequate investigation to cover up their own negligence.

For Mr. Kaczynski’s supporters, it has become an article of faith that the crash was no accident. Instead, it reinforces ancient realities: that Poland still faces a threat from Russia to the east and should remain wary of the great powers to the west that have betrayed Poland in the past. When the governing party declares that Poland’s sovereignty is under threat, the smoking plane wreckage in the Russian woods is considered proof.

A few weeks ago, tens of thousands of supporters gathered in Pilsudski Square in Warsaw to commemorate the eighth anniversary of the crash. A new monument to the 96 people killed in the crash was unveiled — a block of solid black granite, with 18 stairs carved into the stone, a symbol of both the stairs leading onto the plane and of a stairway to heaven.

The Law and Justice party has spent years trying to discredit the findings of the earlier inquiries and, since taking power, government prosecutors have ordered the remains of nearly all the victims of the crash exhumed — sometimes without even informing the families of the victims. As the anniversary approached, officials promised that they would present new evidence that would reveal the truth.