America’s founding fathers drew inspiration from the solid virtues and libertarian zeal of the Roman Republic. These days, comparisons with Rome’s later periods of imperial excess and hubristic over-expansion are more popular. Some point to Rome’s institutional decay, when emperors allowed palace insiders to sideline the senate. Others dwell on its military misadventures, in particular the perennial failure to subdue Mesopotamia.

Now the US comptroller general has joined the fray, crying that moral decline, military overstretch and spendthrift fiscal policy could sow the seeds of America’s ruin. His comments fuelled a blogging frenzy. The question “Are we Rome?” – long a national fascination – has become shorthand for “Are we doomed?”

Any lobbyist can find a parallel to serve his purpose in the comparison. Anti-immigration campaigners can claim Rome fell through an over-reliance on German mercenaries. Protectionists might argue the sapping effects of a parasitic consumer economy sucking in imports. Other theories for Rome’s decline fit the US less well: Christian pacifism, for example, or measles.

Yet Edward Gibbon, whose Decline and Fall started the ball rolling, pointed out Rome’s destruction was less remarkable than its long survival. Rather than lamenting a slide into decadence, the US could remind itself of strengths it shares – social mobility, an ability to assimilate newcomers of different races, and a talent for making life pleasant for its citizens, whether with aqueducts or circuses.

One difference, though, remains clear cut. Rome explicitly assumed that an aptitude for administration justified its pursuit of world empire. The US, whose rhetoric of freedom and democracy implies a similar sense of civilising mission, denies having any imperial ambitions. And while Rome succeeded in spreading prosperity around the Mediterranean, US interventions are breeding new enemies.

If Washington wants to match Rome’s longevity, it should look to its achievements, not to its failings.