Can you imagine Republican House Speaker Dennis Hastert and Senate Majority Leader Bill Frist proudly standing beside President John Kerry in a Rose Garden signing ceremony as he signs a bill that they handed him - a bill that will increase government spending over the next decade by more than half a trillion? Especially if that bill would give Democrat Kerry the loyalty of a politically powerful constituency?

Of course, the GOP's congressional leadership did help President George W. Bush - their own party's man - pass his Medicare bill, whose projected costs keep rising above that budget-busting level. In fact, Bush, with the exception of his tax cuts, has been a shockingly big-government conservative.

It's an insight of libertarianism and a key reason this newspaper does not endorse candidates for office that politicians can't be trusted to deliver on the principles they might verbalize. In fact, politicians can be trusted only to be politicians, to work for partisan advantage and more political power.

That's why, in the context of November's election, a victory for Kerry, who will finally officially become the Democrats' standard-bearer in Boston this Thursday - even though he's a big-government man all the way - could paradoxically be the most likely hope for curbing excessive government growth in the next four years. Why? The party stereotypes don't always hold up, and a Democratic president and a Congress led by Republicans creates a kind of institutional impasse that actually slows the momentum of government.

It seems counterintuitive, though, to expect limited government from a Democratic president. Ever since the Goldwater vs. LBJ contest of 1964, the two major parties have staked out rough philosophical positions along these lines: the Republicans are, at least rhetorically, for a lean and limited government; the Democrats are unreconstructed advocates of state power, state spending and state solutions to every problem.

But the facts - the performance of the parties when they have the power - have never borne that out. We got such regulatory state measures as the Clean Air Act and wage and price controls under Nixon, and the Americans with Disabilities Act under the first George Bush. And it was under Democrat Bill Clinton that we got meaningful welfare reform that has knocked nearly 3 million families off the federal dole so far, even as child poverty rates shrink.

But the most vivid example that Republicans can't be relied on as consistent defenders of smaller government is our current Republican president. Bush has increased domestic discretionary spending 25 percent in less than four years, compared to an increase under Clinton over his entire two terms of only 10 percent.

Bush's administration is spending over $20,000 per American household, the highest level, adjusted for inflation, since World War II. He can't blame it on war and post-9/11 security measures alone, either. Even with those taken out of the equation, according to an analysis by the usually GOP-leaning Heritage Foundation, discretionary spending under Bush has increased 16 percent, from $340 billion to $395 billion.

And then there's his Medicare expansion. Clinton had an opposition Congress to curb his health-care expansion enthusiasms; Bush, alas, had a GOP Congress mostly compliant to his wishes.

Bush has betrayed the humble, restrained small-government vision of the Republican Party in other ways as well, for example, by engaging in a spectacularly expensive nation-building project in Iraq, despite talking intelligently against that sort of big-government hubris while campaigning in 2000. He's shown no firm dedication to free-trade principles, hiking tariffs on steel and shrimp. He's supported restrictions on free political speech by signing the McCain-Feingold campaign finance reform bill.

This is not to say a Republican Congress (which seems very likely to stay Republican after November) will always have the clout to stymie any tax-raising, big-spending, big-program instincts Kerry may have. But it seems reasonable to assume that it would.

Given the likely results of 2004's congressional elections, Kerry's desires to be a bigger-government president than Bush will doubtless be curbed through the logic of partisan conflict and "divided government" - when the executive and legislative branch are controlled by opposing parties.

Nothing is certain when contemplating the political future. But we do know some things about the recent political past that should help guide a strategic voter who wants smaller government: In the past, divided government has shown great power to curb federal spending. As William Niskanen, a former chairman of President Reagan's Council of Economic Advisers, has noted, the only two post-World War II periods of genuine restraint in federal spending growth (with annual increases of less than 1 percent) came during the Eisenhower and Clinton administrations. Both presidents mostly lacked Congresses controlled by their parties.

It couldn't be clearer that the combination of Bush in the White House and a GOP-dominated Congress has been a disaster when it comes to curbing the growth of government spending and programs. It might just be that partisan spite can make a Republican Congress do the right thing where a principled dedication to reining in government seems MIA. When GOP lawmakers don't have the political reputation of their party's standard-bearer to protect, they are more likely to stiffen their spines and help obstruct much of the damage that John Kerry might attempt.

And if George Bush doesn't receive some electoral punishment for his profligate ways, the Republican Party's value as a vehicle for limiting government will plunge lower than a 10-year-old Ford Escort. Bush might earn some short-term electoral advantage through expensive schemes like his Medicare reform. But such schemes are sure to bankrupt the republic in the long run. His own party's Congress won't stop him. They just might stop President John Kerry.

As paradoxical as it seems, for those who believe in the Republican Party that Barry Goldwater and Ronald Reagan promised, Kerry may be their greatest realistic chance to express their support for preserving that tradition.