WHAT THEY DON’T KNOW CAN HURT THEM…. Evidence of an “enthusiasm gap” between Democratic and Republican voters is hardly new, though it may prove to be one of the year’s most important campaign dynamics. Recently, the trend became even more evident.

Gallup’s latest poll measuring partisan enthusiasm not only showed Republicans with a sizable advantage, but found that excitement among GOP voters has reached a level with no modern precedent.

This week’s report from the Pew Research Center found a similar partisan landscape: “Fully 56 percent of Republican voters say they are more enthusiastic about voting this year than in previous elections — the highest percentage of GOP voters expressing increased enthusiasm about voting in midterms dating back to 1994…. The Republican Party now holds about the same advantage in enthusiasm among its party’s voters that the Democratic Party held in June 2006 and the GOP had late in the 1994 campaign.”

And 1994 proved to be a rather consequential year, as I recall.

But to me, that wasn’t the most interesting part. This was. (via Suzy Khimm)

…Democratic voters this year are not particularly pessimistic about the election: 29 percent expect the Democrats to do better in this year’s midterm, far more than the percentage of GOP voters who said that four years ago (16 percent). Nearly half of Democratic voters (48 percent) expect the party to do about the same this fall as in recent elections, while just 18 percent say it will do worse.

Wait, wait, wait. Democratic voters aren’t nervous?

This is, of course, just one poll, and I haven’t seen other outlets asking the same question, so it’s hard to say with certainty just how widespread these attitudes really are.

But the Pew Research Center is a fairly reliable outlet, and if its reporting on this is accurate, it’s really important.

Democratic candidates excelled in 2006, and had another terrific cycle in 2008. It’s certainly possible that Pew’s data is correct — Democratic voters just don’t realize, at least not yet, that the party’s gains can entirely disappear this November, giving enormous power to an increasingly radicalized Republican Party.

If less than a fifth of Democratic voters expect Dems to do worse in 2010 than in recent elections, the party has no choice but to make the stakes clear.

To put it mildly, there’s a very plausible chance the Democrats will lose their House majority; control of the Senate is in play; and there’s no shortage of important gubernatorial races and ballot initiatives. There’s also the consequential matter of post-Census redistricting — the more Republicans are elected to state legislatures, the more lines will be redrawn to help GOP congressional candidates.

Republican voters, according to multiple polls, are practically counting the days until November, almost desperate to elect far-right candidates. If rank-and-file Dems seriously believe their party is positioned to do well — indeed, if nearly a third of these Dems expect the party’s candidates to do better than usual — they’re living in a fantasy world.

The awakening next January will likely be a rude one — intractable gridlock, endless and pointless investigations, and a progressive policy agenda brought to an immediate halt. Hell, presidential impeachment might even find itself on the table.

This expectations problem is not lost on party leaders.

Architects of President Obama’s 2008 victory are braced for potentially sizable Democratic losses in November’s midterm elections. But they say voters’ unease about a GOP takeover will help their party maintain congressional majorities.

“I think the prospect of a Republican takeover — while not likely, but plausible — will be very much part of the dynamic in October, and I think that will help us with turnout and some of this enthusiasm gap,” said David Plouffe, who was Obama’s campaign manager two years ago and is helping to oversee Democratic efforts this fall. Still, he put all Democrats on notice, saying: “We’d better act as a party as if the House and the Senate and every major governor’s race is at stake and in danger, because they could be.”

That sounds about right. If Democratic voters realize that a radicalized GOP is poised to make significant gains in November, Dems are more likely to show up to prevent that from happening. The combination of Democratic successes — breakthrough legislation on health care, student loans, Wall Street safeguards, etc. — and Republican hysteria seems like a capable antidote to the enthusiasm gap.

But that means the party has quite a bit of educating to do over the next four months, because if Pew’s research is correct, the Democratic rank-and-file has no idea how devastating the elections might be.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.