DES MOINES, Iowa — For decades, country and city interests had come together every few years to pass the farm bill, a measure that provided billions of dollars in subsidies to farmers and businesses in rural areas and food stamp money for urbanites.

No more.

The recent defeat of this year’s farm bill — traditionally a sturdy, albeit lonely pillar of cooperation in Washington — highlighted how the country-city political marriage became yet another victim of partisan politics in polarizing times. The divorce throws into doubt the future of sweeping agriculture and nutrition spending.

Here’s how the breakdown of a longtime coalition happened: Newly emboldened conservative groups pressured rural-state Republicans — many representing agricultural districts — with radio ad campaigns to oppose the five-year $940-billion bill, calling its proposed cuts to food stamps too little. Hardly faultless, Democrats, whose districts mostly encompass urban areas home to food-stamp recipients, refused to budge on cuts they considered too deep. Each party was fearful of angering their core supporters.

It was the height of partisanship over a measure that long had been devoid of it.

“That kind of thing wouldn’t have happened at another moment in time,” said Rep. Allyson Schwartz, a Pennsylvania Democrat who opposed the measure.

Rep. Steve Daines, R-Mont., voted for it, and bemoaned the result of House failure to pass it: “Doing nothing is worse than doing something.”

Traditionally, Democrats and Republicans have worked closely together to pass farm bills.

Long ago, conservative rural lawmakers whose numbers in Congress were shrinking became aware that they alone couldn’t muster enough votes to pass a measure paying for farm programs. So they agreed to include food-stamp money in the farm bill in exchange for support from their more liberal urban peers.

It was a mutually beneficial relationship. Conservative lawmakers were mindful that the measures included subsidies for farm-growing regions home to their core constituents, while liberal lawmakers were keenly aware that they contained dollars for food assistance that largely went to their bedrock voters in big cities. Each party needed the other to pass the measure that melded both farm and food money, and it almost always passed with bipartisan support.

But this year, when House Speaker John Boehner urged lawmakers to support the bill and put it up for a vote, it failed to get enough support, shocking longtime congressional observers and lawmakers alike. Tea Party-backed conservatives refused to budge in their demands for even deeper cuts to the food stamp program, which has doubled in cost over the last five years to almost $80 billion annually and now helps feed 1 in 7 Americans.

The House version already had proposed slashing the $955 billion version of the bill that the Democratic-controlled Senate had passed by $20.5 billion in food-stamp cuts. That wasn’t enough for some Republicans and their allies, who were looking ahead to the 2014 midterm congressional elections and worried about the impact of supporting the measure.

“I can’t imagine being a Republican and asking primary audiences for their vote when you just voted for this debacle,” said Americans for Prosperity President Tim Phillips. “It’s impossible to justify, no matter where you are from.”

Lawmakers like Rep. Walter Jones, R-N.C., who voted for the $600 billion farm bill in 2008, were clearly mindful that they would be inviting this type of criticism if they backed this year’s measure. The congressman, who often talks about his district’s tobacco, cotton and soybean production, chose not to take that chance. He voted against the bill after Americans for Prosperity targeted him with radio ads and an email push to contact his office.

Jones explained his “no” vote this way: “At a time when America is over 16 trillion dollars in debt and running massive deficits, we simply cannot afford this.”

Republican Rep. Phil Gingrey, who has represented rural Georgia during his decade in Congress, also voted against it. One of his advisers argued that the measure didn’t do enough to benefit farming. But the adviser, Chip Lake, also noted the increased pressure from outside groups, saying, “That activity between the last farm bill and this farm bill has increased exponentially.”

For example, the conservative group Heritage Action urged constituents to call lawmakers like Rep. Tom Latham, a 10-term Iowa Republican, to pressure him to oppose the measure. Latham, as a result, received calls from constituents angry about the bill’s food-stamp spending. Latham aides said the calls frustrated the congressman. He had argued that, without the cuts, food-stamp spending would be unchecked.

If no bill passes, Congress would likely adopt a short-term resolution to continue spending at current levels.

Democrats, meanwhile, were fearful of backlash from liberals who warned them against voting in favor of deep food-stamp cuts.