For months, voters have been barraged by claims and counterclaims from Republicans and Democrats about the degree to which the landscape is shifting in the race for control of the Senate, which polls are correct and who has the best voter turnout operation. Get ready for more, and be wary about what you hear.

Two narratives have competed for attention since Campaign 2014 got underway.

One says, rightly, that the political environment favors the Republicans. Voters are unhappy. Most of the competitive races are in red states. President Obama’s approval ratings are weak. Democrats usually struggle to get their voters to the polls in midterm elections.

The second narrative says: Hold on, it’s not over yet. The reasons? Democrats have some popular issues on their side, from raising the minimum wage to their positions on women’s issues. Republicans have to beat a bunch of Democratic incumbents to win the six seats needed to take control in January. Some Democratic candidates have outperformed expectations.

What’s been happening over the past two weeks feeds both sides of the debate. For example, Republicans are talking up their prospects in Alaska, Arkansas, Iowa and Colorado. Not that those races are put away by any means, but Republicans see evidence that makes them optimistic. Based on earlier assumptions about which states were actually in play, GOP victories in those four states would spell doom for Democratic hopes of maintaining control of the Senate.

Election Lab: See our current forecast for every congressional race in 2014

But wait. Democrats have suddenly decided to put $1 million into South Dakota, a state that until this week was considered a certain pick-up for the Republicans. Could that state actually be in play? In Kansas, Republican Sen. Pat Roberts remains on the defensive, though in a rock-ribbed Republican state that hasn’t elected a Democrat to the Senate since the New Deal. Republicans also are stepping up their advertising in Georgia. A GOP loss in any of those races could scramble predictions about who will control the Senate in January.

Adding to the “it’s not over yet” side of the competing narratives, Democratic pollster Stan Greenberg said last week his latest survey in the Senate battlegrounds shows perceptible trends that suggest movement toward the Democrats.

Republicans remain skeptical about such claims, and Democratic hopes for maintaining control, however, still may rest on the ability of Vice President Biden to break a tie in a 50-50 chamber.

Conflicting data

The final three weeks of the campaign will produce a flurry of new polls. For consumers of all this political information, some caution is in order. Ask political strategists who have been in the cockpit of campaigns in the closing days of past elections and many will tell you they don’t pay much attention to the public polls. They prefer the polls they commission and pay for.

Comparing public polls is sometimes apples to oranges. For example, a Marist poll for NBC News completed on Oct. 1 showed independent Greg Orman leading Pat Roberts in Kansas by 10 points. A poll completed five days later by CNN/Opinion Research showed Roberts ahead by one point. A poll completed a day after that for Fox News put Roberts up by five points.

People running campaigns argue that they put more confidence in data when they know the methodology behind it and when they can track changes through a series of surveys with consistent methodology.

But the public polls are not at all irrelevant, particularly when looked at in groups. The 2012 campaign should have taught this lesson to everyone.

Republicans dismissed many of the public polls showing the president ahead of former Massachusetts governor Mitt Romney as either skewed by their samples or within the margin of error. Some skeptics of those public polls argued that an Obama lead within the margin of error theoretically could mean Romney was actually a point or two ahead.

But however narrow the margin, when a candidate leads in virtually every poll in the weeks before an election, as Obama did, that should suggest that, while the candidate does not have a guarantee of success, he or she probably has an actual advantage, however small.

The Real Clear Politics compilation of polls in key races currently shows Republican Dan Sullivan ahead of Democratic Sen. Mark Begich in five of the most recent five polls in Alaska; Republican Tom Cotton ahead of Democratic Sen. Mark Pryor in four of the last five polls in Arkansas; Republican Cory Gardner (who just won the endorsement of the Denver Post) ahead of Democratic Sen. Mark Udall in three of the last four polls in Colorado; and Democratic Sen. Kay Hagan ahead of Republican Thom Tillis in all of the five most recent polls in North Carolina.

That’s not to say that all these races will end up the way they now look, only to suggest that, while no single poll tells the whole story, collectively they are not meaningless. As one Democratic strategist put it, public polling does have some influence — when people think a certain candidate is going to win, he or she often wins.

The probability models have caused some confusion this year because they sometimes varied widely on the likelihood of Republicans gaining control of the Senate, though they’ve consistently pointed in that direction.

The Washington Post’s Election Lab, which uses modeling to predict the outcome, now says that there is a 95 percent probability that Republicans will end up with the majority in the Senate. Other models put the GOP’s chances at better than 50 percent but well short of Election Lab. The New York Times’s model pegs it at 65 percent, while Nate Silver’s FiveThirtyEight says it’s a 58 percent probability.

On Friday, my colleague Chris (“The Fix”) Cillizza wrote a headline on his blog post that said, “The Washington Post’s election model gives Republicans a 95 percent chance of winning the Senate. Um, what?” It’s worth reading Cillizza’s exchange with John Sides of George Washington University, who runs the Monkey Cage blog and oversees Election Lab, to understand better how and why the model came to this outcome. (Excerpts can be found on Page A6.)

Democratic pollster Mark Mellman offers another smart analysis of these models in a column he wrote this past week for The Hill. He writes: “What these numbers may mean is that it is a bit more likely that the GOP wins control of the Senate this cycle than that Democrats keep it.”

The final push

If many of these Senate races are as close as they now appear, get-out-the-vote operations could tip the balance in one direction or another. Between now and Nov. 4, Democrats and Republicans and an array of outside groups will boast about their ground games. Even they can’t say with certainty that theirs is better than their opponents’.

Campaign strategists will offer up impressive metrics of how many doors have been knocked by their volunteers, how many phone calls have been made from their phone banks, how they have precision targeting models and how what they are doing this election far surpasses anything done in the past.

All of that likely is true. The sophistication of today’s campaigns is impressive and much better than it was two decades ago. There is far more information known about the electorate and many more ways to reach specific voters. But the proof is in the results.

In 2012, it was clear, except to some Republicans, that Obama had a better voter identification and turnout operation than Romney. But that’s not always the case. As one veteran campaign strategist told me Friday, Election Day provides the proof, and the judgments can be harsh. “The winner has a good ground game,” he said, “and the loser doesn’t.”