In a tough economic speech this morning, John McCain warned that Barack Obama would empower a "dangerous threesome" with unchecked power to enact a liberal agenda of taxing and spending. The other members threesome, of course, would be House Speaker Nancy Pelosi and Senate Majority Leader Harry Reid.

McCain is not the first conservative to make this argument. His allies have been making similar statements, with increasing urgency, for the last few weeks. But I wonder just how well it will work.

For one thing, it's not clear how much the public even agrees with the substantive argument. Nobody likes paying more taxes and, at least in theory, most people are wary of big government. But, according to the polls, most people believe (rightly) that Obama's tax cut does more for the middle class and poor. And while they may not like "spending," they do want better schools, investment in new jobs, universal health care, and so forth. 

The liberal brand, in other words, just isn't as toxic as it used to be. 

Still, there's one other reason this argument might not stick. In the past, arguments like these have worked because they could focus on polarizing Democratic icons. And, at least in recent years, the two icons who worked best for this purpose were Senators Hillary Clinton and Ted Kennedy.

But Clinton's stature has grown. And, particularly since the Democratic primaries, she has proven popular with many of the same voters McCain needs (which is why he's tried so hard to court them). Kennedy's public image may not have changed as much. But his bout with brain cancer pretty much makes him off limits for attacks.

So who in the Democratic Party is left to demagogue? Howard Dean is the next name that comes to mind. But he's on his way out of Washington anyway. That leaves Pelosi and Reid. They simply don't have the same notoreity, if only because they haven't been the focus of sustained national attention the way Clinton and Kennedy have been. 

*Shameless play for Google traffic. 

--Jonathan Cohn