When the Republican chairman of the Senate Foreign Relations Committee, Arthur Vandenberg, offered his backing in 1948 for Democrat Harry Truman's establishment of NATO, he declared that "politics stops at the water's edge".
On this side of the Atlantic, we've largely adhered to Vandenberg's maxim and there has been a consensus between Labour and the Conservatives on foreign policy in the post-Cold War period. That's been most evident in the Middle East. In the 1990s, Labour backed the Major government when it set its face against western intervention as the former Yugoslavia descended into civil war, while the Tories backed Tony Blair's decision to go to war in both Afghanistan and Iraq.
Trying to carve out a distinctive position, the Liberal Democrats adopted a hawkish stance on Yugoslavia but a doveish one on Iraq.
Ed Miliband's forceful attack on the government's handling of the conflict in Gaza suggests he has few qualms about breaking the hitherto broad unanimity between the Tory and Labour front benches. Indeed, this is the second major break - following the Opposition's decision to "stop the rush to war" in last August's parliamentary vote on Syria - Miliband has instituted in just under a year.
In terms of policy, the gulf between the two sides isn't wide: like Miliband, David Cameron has consistently called for a ceasefire. But, tonally, the breach over Operation Protective Edge has been growing as the Prime Minister places the onus largely on Hamas, while Labour appears to suggest that Israel bears greater responsibility for a conflict that shadow foreign secretary Douglas Alexander says "shames our common humanity".
Raw politics won't be entirely absent from Labour's calculations. After a difficult summer, Miliband received a major fillip inside the party for his stance on Syria. He continues to trumpet defeating Cameron's plans for air strikes as one of the major achievements of his leadership and evidence that the party has "moved on" from New Labour.
The politics of Gaza, though, has an added complication for Miliband. On Syria, Nick Clegg was a leading proponent of military action. However, over the past month, the Deputy Prime Minister has been at the forefront of criticisms of Operation Protective Edge, suggesting that Israel has "overstepped the mark", calling for it to open direct talks with Hamas, and pushing for Britain to suspend arms export licenses.
Clegg's stance carries minimal political risks: there are few strongly pro-Israel voices within his party. Attacking Israel provides an opportunity for him to polish his tarnished centre-left credentials.
This is space that Miliband will be loath to concede to Clegg, however. Since becoming Labour leader he has pinned his hopes of making it to Downing Street on holding on to the left-wing voters who defected to the Liberal Democrats over Iraq in 2005 but fled the party when it went into coalition with the Tories in 2010.
Dubbed the "35 per cent strategy" by Miliband's critics, it is threatened by anything which allows the Liberal Democrats to re-establish a connection with the Guardian-reading voters in key Labour target seats.
The Labour leader's position on Gaza is not without risk. Polls may indicate support for his views, but any suggestion that he is playing politics could undermine what the president of YouGov, Peter Kellner, has identified as his key task: to "start sounding like a prime minister-in-waiting rather than a perpetually angry critic of the coalition".
Baroness Warsi's resignation as a Foreign Office minister over the government's "morally indefensible" stance over Gaza will have provided Miliband with some cross-party political cover. But while some see her resignation as a revolt against the more pro-Israeli position of new foreign secretary, Philip Hammond, others detect a more base motive. The former Tory chair had allegedly been told during last month's reshuffle that she wouldn't be promoted beyond her current senior minister of state level.
Nonetheless, some Tories believe the political repercussions of losing Britain's first Muslim female cabinet minister shouldn't be dismissed.
Paul Goodman, editor of the influential ConservativeHome website, argued this week that the Tories shouldn't exploit Gaza for electoral purposes, as he claims Miliband and Clegg are doing. Nonetheless he cautioned: "It's true that most Muslims don't vote Tory and are concentrated in Labour seats. But enough supported the party in 2010 and live in marginals to matter electorally."
With less than a year to go until the election, any chance of Vandenberg's axiom applying to Gaza appears less a statement of fact than so much wishful thinking.