To understand the anomaly of Representative Max Rose, one of the few House D emocrats who has not endorsed an impeachment inquiry into President Trump, one must first understand a few other anomalies.

There is the anomaly of Staten Island, the lone stronghold of conservatism within deep blue New York City, and the heart of Mr. Rose’s district.

There is the anomaly of Mr. Rose himself, whose victory last year made him just the second Democrat to represent Staten Island in Congress in more than 30 years.

All of which leads to the third and current anomaly: Mr. Rose’s refusal to back impeachment, amid revelations that Mr. Trump asked the president of Ukraine to investigate the former Vice President Joseph R. Biden Jr., even as most other Democrats in vulnerable seats have signed on.