Taking Congress back from the Republicans in this year’s midterm elections may be more difficult for Democrats than anticipated, according to recent polling.

A new poll from ABC News and the Washington Post shows Democrats’ advantage is narrowing in a so-called “generic ballot”, where voters are asked which party they plan to favour in the coming election. In January, Democrats lead Republicans in a generic matchup by 12 per cent. In April, that lead was just 4 per cent.

The polls come in advance of the November midterms, when the two parties will battle for control of Congress. The most potential for change exists in the House, where Democrats need to flip just 24 seats to regain the majority. The calculations thus far have looked to be in their favour, as President Donald Trump’s approval ratings hit historic lows and dozens of Republican politicians announced their resignations.

But the ABC/Washington Post results show that lead is narrowing somewhat, with Republicans making sizeable gains among white voters. An average of the generic polls from Real Clear Politics had Democrats leading Republicans by 6.2 per cent on Monday, compared to 9.3 per cent at the beginning of last month.

But political science professor Jeanne Zaino said not to put too much stake in the generic matchups. These generalised polls fail to account for details like specific candidates, and the amount of money and energy dedicated to a race.

“As we start to get closer to the midterms, I don’t find it surprising that we would something of a narrowing, because people do start to consider the issues, the candidates, and that kind of thing,” Ms Zaino told The Independent. “I would never read too much into these generic ballots.”

Ms Zaino said Republicans’ prospects may have been momentarily buoyed by the recent air strike in Syria, and by attempts to play up Mr Trump’s achievements at the end of his first year in office. Democrats may also be turned off by the lack of an identifiable party leader, as liberals jostle for a candidate to lead the pack in the 2020 presidential election.

Ms Zaino also noted that there may be some frustration with Democrats for not taking more action on gun control in the wake of the mass shooting at Marjory Stoneman Douglas High School in February. The ABC/Washington Post poll showed gun control is shaping up to be a major issue in the midterms, with 4 in 10 registered voters saying it is extremely important that candidates share their views.

Democrats have many other factors on their side, however – the first of which being history. Over the last 80 years, the president’s party has usually lost control of Congress in the midterm elections. That effect is strengthened when the president himself is unpopular – a major factor for Mr Trump, whose 38 per cent average approval rating over the last 15 months is the lowest of any president in more than 40 years.

Democrats also have a major lead in voter enthusiasm, which is generally a good indicator of how many people will vote in the election. According to the NBC/Wall St Journal poll, 66 per cent of Democratic voters have a high level of interest in voting in the midterms, compared to just 49 per cent of Republicans. Polling from Pew Research shows 83 per cent of liberals are looking forward to the midterms, compared to 58 per cent of conservatives.

If the actions of Republicans in Congress are any indication, they seem to be fearing a tide of Democratic victories, too. A record 39 Republicans in the House announced they would retire from Congress this year – including Speaker of the House Paul Ryan.

But Ms Zaino preached caution when making predictions from any of the midterm polls.

“Yes the Democrats are up. Sure, we’ve seen the numbers fluctuate,” she said. “But I would hardly suggest that means the Democrats should be celebrating or running in fear.”