His power unbending, his whims often unexplained, Sheldon Silver, in his two decades as speaker of the State Assembly, became a seemingly indestructible presence at the nucleus of the New York political world, a steady advocate for liberal causes and a master tactician in Albany’s closed and entrenched way of governance.

But Mr. Silver’s arrest on Thursday on corruption charges has thrown into question that arrangement, in which the governor and the leaders of the two chambers of the Legislature privately decide the most crucial policies of the state. It is a potentially seismic shift in power whose reverberations may be felt throughout the state, from the speaker’s home district on the Lower East Side of Manhattan to the grounds of the State Capitol.

Until now, Albany lawmakers accustomed to what prosecutors called a “show-me-the-money culture” have taken comfort in knowing that their most powerful figure was unassailable — untouched despite years of inquiries, suspicions and rumors of impropriety.

The events this week have shaken that sense of security and raised the possibility that Mr. Silver, the quintessential capital insider, could reveal his own colleagues’ misdeeds to federal prosecutors in exchange for leniency.