The New York Democrat is continuing to work on his Democratic colleagues, trying to get them to support stiff new sanctions on Iran.

The Hill:

Schumer has long been a hawkish Israel supporter, but the push represents an unusually active challenge to the administration from someone who aspires to lead the Senate when Harry Reid (D-Nev.) retires.

"He's an original cosponsor," said Sen. Mark Kirk (R-Ill.), who drafted the sanctions bill with Senate Foreign Relations Committee Chairman Robert Menendez (D-N.J.). "I would say he probably has the greatest sway inside his conference."

A source close to the effort said Schumer is whipping members in support of the bill, which so far has been publicly endorsed by 59 members: 43 Republicans and 16 Democrats.

And William Daroff, the Jewish Federations of North America's chief lobbyist, tweeted this week that a "VERY reliable source" had told him the bill has the support of 34 Democrats if it comes to a vote - more than enough to overcome the White House's veto threat.

Schumer is running into opposition from some powerful Democrats, however. Ten committee chairmen wrote to Reid in December arguing that "at this time ... new sanctions would play into the hands of those in Iran who are most eager to see the negotiations fail," including the leaders of the Armed Services, Homeland Security and Intelligence panels.

Schumer's office did not deny that he was whipping members when asked directly.

"Members come up to him to ask his views and of course he gives them," said Schumer spokesman Matt House.

Schumer holds considerable sway with Democrats, having overseen a net gain of 14 seats in the Senate as head of the Democratic Senatorial Campaign Committee in the 2006 and 2008 cycles. His successor on the DSCC, Sen. Michael Bennet (D-Col.), signed on as a cosponsor to the sanctions bill on Wednesday.

A source close to the sanctions effort said it wouldn't be surprising that someone such as Schumer is whipping given the unusually large number of people who have quickly signed on as cosponsors since the bill was introduced. The source said the pro-Israel lobby American-Israel Public Affairs Committee held a conference call for donors on Dec. 19, the day the bill was introduced, and told them the sanctions represented a "genuine policy disagreement" with the administration and was "going to be a tough slog".

The sanctions would hit Iran's energy sector with new restrictions if it fails to stop enriching uranium in a final deal being negotiated in Tehran. The White House claims that the threat of new sanctions is hurting those negotiations.

The White House needs some spine-stiffening and the sanctions are designed to do just that. It is extremely unlikely that Iran will halt uranium enrichment so the sanctions are a real threat. The Iranians can use the sanctions as an excuse to break off talks if they want, but the bottom line is that a renewal of energy restrictions will strike a blow at the Iranian economy. It won't get them to change their mind but it will limit how much troublemaking they can do.