In the Senate, where the Democrats need to win only two seats to take the majority? The odds are good that they won’t. In fact, according to the current RealClearPolitics polling averages in the contested races, the most likely outcome at this moment is that the Senate after Nov. 6 will look exactly as it does before Nov. 6: 51 to 49 in favor of the Republicans.

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How is that possible? How could the Democrats benefit from a big wave on one side of Capitol Hill but not the other? For a number of reasons.

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The first is that the deck was always heavily stacked against the Democrats, as we noted in our first look at this question, in December. There are 35 seats on the ballot next month. Twenty-six of those seats are currently held by Democrats or the two independent senators who caucus with the Democrats. In other words, the Democratic Party needs to defend 24 seats — and the Republicans need to defend only nine.

What’s more, the nature of senatorial terms — lasting six years — means that senators face reelection in a different sort of election than when they were elected. If you’re elected in a presidential election year, when the electorate tends to be more favorable for Democrats, you’re up for reelection during a midterm, when the terrain is rougher. Most of those 24 Democrats were last elected in 2012, when Barack Obama’s reelection bid powered turnout. Next month’s electorate will look different.

But the question at hand isn’t why the Democrats are in trouble in general, it’s why their chances look worse now than in recent months.

Here’s the polling average in close Senate races over the past few months.

It’s a bit of a plate of spaghetti, so let’s break it out by party.

First, here are the seats held by Democrats that are currently within a 10-percentage-point polling-average margin.

A few things to note. That North Dakota race has gotten grim for the Democrats, with Republicans moving ad spending out of the state. In interviews this week, President Trump implied that this was an unexpected success story for the GOP, but it’s worth remembering that he won the state by more than 30 points two years ago. Sen. Heidi Heitkamp (D-N.D.) was a beneficiary of the 2012 electorate, and the 2018 electorate seems unlikely to help.

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Notice that the other significantly dangerous race for the Democrats, Missouri, has held fairly steady. Montana, another Trump state, has gotten slightly worse. A few races — Florida, Connecticut and the special election in Minnesota to replace former senator Al Franken — have gotten better.

There are three main takeaways, though. First: There are quite a few Democratic races in this polling range. Second: It’s a mixed bag on how the polls have shifted. Third: The party trails in two contests.

Now compare that with the Republicans.

Four seats in this polling range. Leads in two; tie in one (Nevada). But all four have moved significantly toward the Republican in recent weeks.

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So why the uniform shift for the Republicans but not the Democrats? Perhaps part of it is an energized Republican electorate after the Brett M. Kavanaugh hearings, though you’d expect that to show up in redder states such as Montana and Missouri, too. It may also be a statistical fluke, a function of there being only four races in the mix and the average relying on a smattering of polls in each.

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But the point is simple. If the election were held right at this minute and the polling averages were perfect predictors of the results, the Democrats would lose two seats and the Republicans one.

That’s the Senate. Over on the House side, meanwhile, the best overall indicator of how things are going is the generic ballot, that question in polls in which respondents are asked whether they prefer the Democratic or Republican House candidate in their district. That metric, according to RealClearPolitics’s average, is just puttering along.

What’s more, it’s the Democrats with the structural advantage in the House races. A slew of Republicans, seeing where this year’s elections were trending, have announced their retirements, leaving the GOP without any incumbency advantage in races in which a Republican holds the seat.

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The Cook Political Report estimates that 15 seats held by Republicans are likely to be won by the Democrats, including seven seats without incumbents. An additional 29 seats (including six open ones) are considered too close to call. Remember, the Democrats need to win only 23 of those 44 seats to take the majority.

The outstanding question of the election is this one, from Cook’s Dave Wasserman.

The assumption has been that a flood of Democrats, energized in large part by opposition to Trump, would push everything on the ballot to the left next month. But polls have shown that Republicans are energized, too. The Pew Research Center has energy on the right higher than even in 2010, when the Republicans swept the Democrats into the minority in the House.

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So Wasserman’s two options: a big blue wave that breaks pollsters' forecasting models, leading to Democratic victories even in those Tennessee, Arizona and Nevada Senate races. Or a big blue wave and a big red one, in part bolstering each party where it’s naturally strong.