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'Tightening' races? Or just politics, as usual?

It’s been a recurrent theme throughout the last days of this midterm election cycle: “New poll shows [Insert Senate race that didn’t seem competitive three weeks ago] is tightening.”

According to some polls, candidates in a handful of states have made apparent gains after months of trailing. In Pennsylvania, two new surveys show Democratic Rep. Joe Sestak – who has struggled to stay within striking distance of Republican Pat Toomey since the state’s May primary – now polling within the margin of error. A St. Norbert College/Wisconsin Public Radio poll released Tuesday put Democrat Russ Feingold just two points behind GOP nominee Ron Johnson. In the pricey (and contentious) California Senate contest, a new PPIC poll shows GOP candidate Carly Fiorina catching up with incumbent Barbara Boxer. Gaps have also seemingly closed in Colorado and Alaska.

But what does “tightening” really mean, other than more fodder for analysts dissecting the state of the races?

Experts and pollsters contend it’s a normal part of the campaign life cycle.

“There’s just a natural tightening of races,” says Nathan Gonzales, who analyzes races for the nonpartisan Rothenberg Political Report.

In the final weeks before a competitive statewide election, when activists are working to fire up their base and television audiences face a closing barrage of paid political advertising, voters begin to pay attention.

In this cycle, that especially means Democratic voters.

“The tightening is just mostly about more Democrats showing support for Democratic candidates,” added Gonzales. “There are folks who are calling this ‘a Democratic surge’ – I’m just not ready to call it that."

In some cases, Republicans might have already been mobilized because their side of the political spectrum was simply more interesting early on in their state's campaign contests.

In the Wisconsin Senate race, for instance, Democrat Feingold did not face a contested primary, while Republican candidates in other state races were forced to duke it out for their nominations.

“Democrats and Democratic-leaners just weren’t really all that involved in what was going on politically,” said Dr. Wendy Scattergood of St. Norbert College. “Their side wasn’t where the drama was.”

But now, Scattergood says, those Democrats may be tuning in and rallying behind their nominee.

Television ads could also be playing a role in mobilizing Democratic-leaners – and perhaps changing some minds within the dwindling but crucial bloc of undecided or soft “lean” voters.

Dr. G. Terry Madonna, polling director at Franklin & Marshall College, noted that a series of recent Pennsylvania polls appear to show a slight improvement for Sestak in the Philadelphia suburbs, where Democrats must perform well to retain retiring Sen. Arlen Specter’s seat. That bump, he said, may have been aided by advertisements criticizing Toomey’s vote to normalize trade relations with China. Democrats say the policy has led to job losses in the state.

Madonna says that there does appear to be some tightening in the race but that more independent polling is necessary to prove that the contest is really neck-and-neck. Two polls in the last two days have shown the contest within the margin of error, but various other automated or partisan polls have shown Toomey retaining a high single-digit lead.

While new poll releases are the bread-and-butter of political reporting and analysis, there is some truth to the hackneyed stump line that "the only poll that matters is the one on Election Day." There is often wide variety in how pollsters identify and classify the voters most likely to cast a ballot.

“Ultimately, polling isn’t about how people are going to vote. It’s about who is going to actually show up at the polls,” said Gonzales.

That, he added, is very difficult to predict.