This may be the most important election of our lifetimes, conservative opinion leaders keep insisting. We stand on the precipice of socialism; we can either plunge over or be led gingerly back from the brink by… the governor who pioneered the individual mandate. Oh, and also his running mate, one of “only six Republicans who voted yes on the auto bailout and both bank bailout votes,” as Tim Carney reported yesterday.

In fairness, there are some important differences between Romney-Ryan and Obama-Biden on economic policy. Romney and Ryan at least see the need to downplay their past sins; for President Obama and Vice President Biden, bailouts and mandates are matters of principle and marks of pride.

But on other core questions of federal power — in areas where the president has much more discretion than he does over the budget — there isn’t a dime’s worth of difference between the two tickets. Among those questions: Can the president launch wars at will, subject American citizens to military detention and assassinate them via drone strike?

Over the last two election cycles, Pulitzer Prize-winning reporter Charlie Savage has done a great service by getting all the major party presidential candidates to go on the record with their views on executive power.

One of then-Sen. Obama’s answers to Savage’s 2007 executive-power questionnaire came up quite a bit during the president’s seven-month undeclared war in Libya last year. In 2007, Obama told Savage categorically: “The president does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation.”

That was the correct answer. “In no part of the Constitution is more wisdom to be found,” James Madison summed up in 1793, “than in the clause which confides the question of war or peace to the legislature, and not to the executive department.” Were it otherwise, “the trust and the temptation would be too great for any one man.”

Alas, Obama “evolved,” or — if you prefer — lied. It’s a shame that broken promises like this aren’t taken at least as seriously as breaking a “no new taxes” pledge.

Here, at least, Mitt Romney has been much more forthright than Barack Obama. In Gov. Romney’s response to the war-powers question in Savage’s 2011 survey, Romney promised only to “consult closely with Congress” in a similar situation — and made clear that he considers the War Powers Resolution’s limitations on the president’s power to be unconstitutional. Romney also affirmed he’d be willing to authorize military detention and targeted killing of American citizens.

If you have doubts about the constitutionality of that fearsome array of powers, if you worry about concentrating so much “trust and temptation” in one fallible human being’s hands — and you should — then the 2012 campaign presents a pretty dispiriting choice: Do you prefer a candidate who’s flagrantly violated his promises not to violate the Constitution, or one who tells you right up front that he’ll probably commit the same abuses?

Quite a few conservatives denounced President Obama’s executive power grabs abroad. Many more are rightly concerned about his abuses of federal power on the home front. But the two are connected. You can’t expect the American presidency to operate as the Supreme Warlord of the Earth while abroad and remain a constitutionally constrained chief magistrate at home.

The National Review’s Kevin Williamson put it succinctly after the Supreme Court upheld Obamacare’s individual mandate last June: “A government big enough to whack its citizens with drones is big enough to make them buy health insurance.”