Sen. Charles Schumer (D), the de facto leader of New York's Democratic Party, is throwing his support behind embattled Rep. Charles Rangel (D-N.Y.).

Schumer, whose recent success at picking winners among Democrats is well established,  made a $10,000 contribution to Rangel's reelection campaign in June , breaking what had been a long dry spell of contributions from Democratic lawmakers.

Schumer's support comes at a time when a new poll shows that Rangel is battling for his political survival.

A Public Policy Polling survey released Monday showed Rangel winning less than 40 percent of the vote in a primary race. It showed his job approval at 49 percent.

Adam Clayton Powell IV, Rangel's closest competitor,...