So it's imperative that they be in Washington, and not on the campaign trail, when the Senate votes on Dorgan-Grassley and other subsidy reforms.

Chuck Abbott at Reuters reports (sorry, I can't find it on the Web):

The five senators running for president agree on one reform for the U.S. farm program -- a "hard" cap of $250,000 per farm per year on crop subsidies, a sharp drop from the current $360,000 limit. Proponents say they expect to win a vote on the $250,000 limit, which could come as early as next week. It was the first amendment filed when the five-year farm bill was brought to the floor in early November. In campaign statements and Senate records, the five White House hopefuls -- four Democrats and one Republican -- support the $250,000 limit. The proposal also would close loopholes that allow large operators to evade the current limit of $360,000, set in 2002. Three of the candidates are sponsors of the "hard" cap, Democrat Chris Dodd of Connecticut, Democrat Barack Obama of Illinois and Republican John McCain of Arizona. Democrats Joe Biden of Delaware and Hillary Clinton of New York also support the limit. The issue could be decided in the last few weeks before the Jan. 3 caucuses in Iowa, the No. 1 corn and soybean state. The neighbor gatherings are the first of the state-by-state contests to determine the Republican and Democratic nominees for the Nov. 4 presidential election.