WASHINGTON — With their championship window in danger of closing, the Washington Capitals made a strong move Monday to try to win the Stanley Cup this spring by acquiring defenseman Kevin Shattenkirk in a trade with the St. Louis Blues.

Shattenkirk is a pending unrestricted free agent, but was considered the top rental player available ahead of the NHL’s Wednesday trade deadline.

Washington traded a 2017 first-round pick, forward Zach Sanford, a conditional 2019 draft pick and minor league forward Brad Malone to St. Louis for Shattenkirk and goaltender Pheonix Copley.

The 28-year-old right-handed-shooting defenseman gives the Capitals one of the strongest, deepest blue lines in the league with Shattenkirk, Matt Niskanen, Karl Alzner, John Carlson, Dmitry Orlov, Brooks Orpik, Nate Schmidt and Taylor Chorney. Shattenkirk has 42 points on 11 goals and 31 assists this season and 66 goals and 218 assists in 471 NHL games.

“We felt it was important to acquire another defenseman to strengthen and add depth to our blue line,” Capitals general manager Brian MacLellan said in a statement. “Kevin is a skilled, puck-moving defenseman who we think will help our team at even strength and on the power play.”

The New Rochelle, N.Y., native counts $4.25 million against the salary cap this season. The Blues retained 39 percent of his salary as part of the deal.