As American voters head to the polls, the latest round of surveys shows Democrats favored to retake the House of Representatives and well-positioned for the Senate. Are the United States heading for a protest vote against Donald Trump? Pollsters, however, fear a flaw in their model.

Is a blue wave sweeping the US Congress after Election Day? According to pollsters, this is the most likely scenario for the midterm elections held on Tuesday, November 3. Democrats are expected to regain a majority in the House of Representatives, the Senate, and possibly even both houses of Congress.

Nationally, Democrats have an 8.9-point lead over Republicans. This is calculated using the "generic ballot," which asks voters which party they generally intend to vote for. This indicator is particularly important because the larger the gap, the greater the potential landslide victory in the House of Representatives—assuming the polls are accurate.

Traditionally, the party of the incumbent president loses the midterm elections, and Donald Trump's historic unpopularity, which has now reached 60% according to a poll published Sunday, November 1st by NBC News, also points in that direction.

In the House of Representatives, the Democrats have the advantage.

Since the end of the party primaries in the various constituencies, all opinion polls point in the same direction: a victory for the Democrats in the House of Representatives.

According to the latest projection from the specialized website Decision Desk HQ, dated November 2nd, the Democrats have an 84% chance of regaining control of the House of Representatives. The American website even predicts a sweep, estimating that they will win 241 seats, while only 218 are needed for a majority.

The Cook Political Report, meanwhile, predicts a gain of 12 to 25 seats for a total that could reach up to 240 for the Democrats.

FLIPR, the model by statistician Nate Silver, among the most scrutinized in each election year, gives them a 95.1% chance of regaining possession of the gavel symbolizing the governmental authority of the United States.

In the Senate, a democratic optimism

As for the upper chamber, Democrats have every reason—and all the polls in the world—to be optimistic. Even if the margin is smaller than in the House, pollsters are unanimous in their projections regarding the chances of regaining a majority in the Senate.

Currently, the Senate is composed of 53 Republicans, 45 Democrats, and 2 independents who vote with the Democrats. With 35 seats up for election on November 3, the arithmetic is simple for the Democrats: they need to win four seats to secure a majority. In the event of a tie between the two parties, the Republican Vice President, JD Vance, casts the deciding vote.

Decision Desk HQ estimates the Democrats' chances of winning with 52 seats at 62%. Nate Silver assesses the Democrats' chances at over 80% in his final estimate.

The latest poll conducted by the New York Times with Siena University, published Sunday, November 1, however, estimates that Democratic candidates are now favorites in most of the key states that will determine control of the Senate: Michigan, Kansas, Texas, Maine, Ohio and, by a narrow margin, Alaska and Iowa.

The signs are positive for a blue wave, but...

However, a poll is not an election. Caution is still advised, as polls have repeatedly underestimated the mobilization of Donald Trump's MAGA base in the past.

The venerable Washington Post admitted Friday that it had encountered this phenomenon in Kansas when it conducted a poll that showed the Democratic Senate candidate leading by 9 points. "There is good reason to suspect that this poll overestimates support for Democratic candidates," the newspaper stated.

The New York Times, a competitor, expressed similar caution when publishing its latest poll: "It's a very real possibility. Supporters of President Donald Trump are relatively reluctant to respond to polls, which carries the ever-present risk of polling error. And as we'll see at the end of this newsletter, there are signs that this is once again a serious problem for polling organizations in this election cycle."