What’s the reason for this gulf between popular and congressional opinion? In part, it’s because hawks are more mobilized. An ultra-hard line against Iran has been near the top of the agenda of AIPAC—and pro-Israel political action committees—for two decades now. AIPAC supporters distribute their money to both parties.* But in recent years they have been joined by GOP billionaires, like Sheldon Adelson, who have been liberated by the Supreme Court to spend vast sums for the purposes of shifting the Israel and Iran debates further right. Tom Cotton alone got more than $2 million from these Iran hawks in his 2014 Senate run.

Doves often decry this, but the bigger question is: Why can’t they compete? MoveOn.org and a variety of other progressive groups recently sent a letter warning Democratic senators not to kill the Iran deal. And in the absence of Israeli-Palestinian negotiations, Iran has moved near the top of J Street’s agenda. Still, the discrepancy between the political pressure being exerted by hawks and doves is stunning. A GOP senator who supported the Iran deal would become a virtual pariah in his party and quite likely face a primary challenge—despite the fact that a plurality of rank-and-file Republicans support the deal. In the Democratic Party, by contrast, where public support for last Thursday’s agreement is overwhelming, Charles Schumer can vocally endorse the Corker-Menendez bill, which might well scuttle the Iran deal, without at all imperiling his rise to Senate Majority Leader.

More than a decade after the invasion of Iraq, despite the disasters that American military intervention has brought, there is still a culture of impunity for Democratic politicians who defy their party’s voters on questions of war and peace. Of the 29 Democratic senators who voted for the Iraq War, only one, Joe Lieberman, faced a serious primary challenge. Yes, Hillary Clinton’s Iraq vote helped doom her presidential chances in 2008. But after questioning her foreign policy judgment during the campaign, Barack Obama named her secretary of state, where she joined Vice President Joe Biden, who had also backed the war, and was succeeded by John Kerry, who had too. Since her time as Secretary of State, Clinton has left little doubt that she remains more hawkish than both Obama and most Democratic voters. Yet it looks unlikely an anti-war candidate will challenge her in the 2016 primaries.

There are several reasons for all this. It’s partly because when it comes to foreign policy, conservative donors are more single-minded than liberal ones. Every Republican politician knows that Adelson conditions his checks on their Iran vote. Even dovish Democratic donors, by contrast, generally care about issues like abortion, gay marriage, gun control and climate change, which makes them more willing to donate to Schumer or Clinton despite their differences on Iran.