As the presidential race tightens, Democrats and their supporters are working vigorously to define radical down. In his Bloomberg View column today, for example, Jonathan Alter warns that even if GOP presidential nominee Mitt Romney seems moderate now, he won't possibly govern that way. That's because radical Republicans in Congress wouldn't let him. "The Republicans have become the most extreme major political party in generations," he writes. "They are tolerating Romney's heresies this month only to gain power." Including Maine Senator Susan Collins and Massachusetts Senator Scott Brown, who may not win reelection, Alter argues that "the moderate Republican caucus in Congress might include just two senators, plus three or four House members. That's it."

Alter isn't the only one pushing the line that today's GOP is too extreme to govern. You can find former Clinton administration labor secretary Robert Reich making an extremely similar argument, saying that "today's Republican Party is more radical and extreme than it's been in more than 80 years." Democratic operatives are pushing the same line about various GOP targets. A spokesperson for the Democratic Senatorial Campaign Committee told CNN that Tom Smith, a Republican Senate Candidate in Pennsylvania whose race is currently tied according to Rasmussen, "is a radical tea partier in the mold of Todd Akin and Richard Mourdock." Here's how radical Smith is on the high-priority issue of Medicare:

Obama's campaign has worked hard to paint Romney as a super-scary political radical, with senior campaign adviser David Axelrod warning that Romney and his running mate Paul Ryan share "extreme" views on government, and arguing that the two share politival views that are way outside the mainstream. It's silly for a number of reasons. It's not just that Romney is clearly not some red-eyed radical but instead a managerial technocrat who, among other things, worked hard to pass a state-level version of ObamaCare. It's that the administration is making this argument at the same time that the president's key line of attack on the GOP contender revolves around a gimmicky bit about "Romnesia," in which Romney can't really be trusted because he doesn't have any principles. So which is it? Is Romney some crazy ideological firebrand? Or is he an unprincipled political striver with no particular attachment to principle?

One response might be that it doesn't matter if Romney is an extremist because his willingness to go where the political winds blow will make him a puppet of radical Republicans in Congress. The same radicals, presumably, who have spent the last three years declaring their opposition to President Obama's Medicare cuts, who proposed a balanced budget plan so strict that exempted Medicare and Social Security, and who offered a debt deal so apocalyptic that it called for federal spending to continue to rise. And the same radicals who have rallied around Romney, who is so serious about spending cuts that he has promised to cut federal subsidies to the National Endowment for the Arts and Planned Parenthood, which would save a little less than $500 million out of a $3.7 trillion budget.

Even if you buy this idea, however, it's essentially moot if Republicans fail to win a majority in the Senate. It's not impossible that the GOP will gain control of the upper chamber, but I wouldn't bet on it, because right now the polls are stacked against them.