New polls show Democrats with 10, 12 and 14-point leads over Republicans in the midterm congressional elections — a possible indication of a "blue wave" this fall.

But it's not entirely clear whether this imbalance will hold — the Democrats' advantage over the GOP has swung from single digits to the teens this year.

Democrats had massive 1o, 12, and 14-point leads over Republicans in the midterm congressional elections, according to three new polls of the generic House ballot released Wednesday.

An NPR/Marist Poll conducted during the second week of September found that 50% of registered voters would cast their ballots for Democrats and 38% would vote for Republicans if congressional elections were held then. Another poll, conducted by Quinnipiac University during roughly the same period, found that Democrats have a 14-point lead over their Republican opponents. And a third Politico/Morning Consult poll found Democrats 10 points ahead of the GOP.

No demographic group approves of the job Congress is doing — and 72% of Americans overall disapprove of the lawmakers, according to the Quinnipiac poll. While 58% of voters say Congress should act as more of a check on President Donald Trump, 56% of all voters don't want the body to begin impeachment proceedings against the president.

A late August Washington Post-ABC News poll also found that Democrats have a 14-point advantage over Republicans in the 2018 midterm elections. Just 38% of registered voters said they would vote for Republican House candidates, while 52% said they'd vote for Democrats.

Many observers pointed to the polling as further evidence of a "blue wave" in the midterms this fall. In the last three midterm elections — 2006, 2010, and 2014 — the party in the White House saw massive losses in Congress. Many analysts believe that if Americans' dissatisfaction with Trump and his party remain high, Democrats will flip the 23 seats they need to take control of the House, and possibly the two US Senate seats they need to control the upper chamber.

Quinnipiac University surveyed 1,038 voters across the country between September 6-9 with a margin of error of plus or minus 3.7 percentage points. The NPR/Marist poll surveyed 949 adults between September 5-9 and has a margin of error of plus or minus 3.6 percentage points.