YouGov pollster plays down talk of a blue wave sweeping away Republican majority: ‘Democrats have to win seven of the nine. I think the odds of that happening are not good’

Democrats aiming to take the US Senate in November need results “more shocking than Trump winning the 2016 election”, a leading polling expert said on Monday, playing down expectations of a blue wave.

Democrats lead Republicans nationwide by 54% to 46%, enough to take 225 seats and claim a narrow majority in the House, according to YouGov data released at the Hoover Institution, a conservative thinktank in Palo Alto, California.

In the Senate, where Republicans currently hold a narrow 51-49 majority, 10 incumbent Democrats are defending states that Donald Trump won in 2016. “The chances of the Democrats winning all of those seem to me pretty slim,” Doug Rivers, chief scientist at YouGov global polling, told reporters.

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“You need a wave where all the toss-ups essentially go one direction and then Democrats need to pick up two more seats to get a majority.

“There’s a rather good opportunity in Tennessee, Nevada and Arizona, and then the long shot, which would be a catastrophe for the Republicans, would be Texas. I don’t think the math adds up for a change. That would be more shocking than Trump winning the 2016 election.”

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Rivers, a political science professor at Stanford University, noted that Democratic turnout in recent special elections has been “off the charts” and predicted there was a 75% chance of Democrats taking the House. “But as we learned in 2016, 25% events occur,” he added.

Trump has a 40% job approval rating less than two months before the midterms, according to Gallup, and is seen as a potential drag on Republicans’ fortunes in the House, especially among independents – voters with no party affiliation – and women.

The president’s recent troubles, ranging from an anonymous op-ed by a senior administration official in the New York Times to the supreme court nominee Brett Kavanaugh facing sexual assault allegations, have led to a recent surge of Democratic optimism that the Senate might also be in play. The Republican senator Ted Cruz faces a surprisingly stiff challenge from Democrat Beto O’Rourke in Texas.

But Lanhee Chen, a research fellow at the Hoover Institution, said: “I think Republicans will hold on to and expand their majority in the Senate. The House side I’m not sure about. It’s not as easy as, ‘Oh, the Democrats are going to win a bunch of seats.’ It’s too early to tell. We’ll know a little better in three or four weeks.”

Chen, former policy director for Mitt Romney’s presidential campaign in 2012, suggested that the likelihood of deep red states suddenly turning blue is overblown.

“At the end of the day there are a set of fundamentals here that I think you have to return to when you think about what’s going to happen, and you [would] have to accept the theory that Democratic turnout is going to be so big that it’s going to completely eviscerate what we know about who lives in these states.

“Which is not to say there isn’t concern about a state like Tennessee, for example. It’s just to say when you really take a deep breath and think … Texas is not going anywhere, guys. That’s now what I come back to: what do these states live like? Who lives there?”

While the progressive base is expected to turn out in force, energised by its first chance to impose some checks and balances on Trump, it remains unclear how many independents will join them.

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David Brady, a political science professor at the Stanford Graduate School of Business, said: “I think the Democrats will take the House but at this point I don’t see a wave election where it goes to 230 or 240 or something like that, precisely because I don’t see the independents moving that way yet.”

Nine Senate races are too close to call. Brady added: “What you look for this time is an anti-Trump movement and I’m not seeing that yet among independents. I don’t even see it much among Republicans. Republican women are still saying on the generic ballot they’ll vote Republican at House level.

“In order to take the Senate, Democrats have to win seven of the nine. I think the odds of that happening are not good.”

But Brady also noted a recent YouGov poll finding that just 49% of people who approve of Trump’s presidency want him to run for the White House again in 2020.

“There’s a number of people who like the results that happened so far – less regulation, et cetera – but they don’t like him,” he explained. “There is unanimity among Americans on one thing: vast majorities of Democrats and Republicans would like to see him stop tweeting.

“So I think what happens is even if people like what he’s doing there are many Republicans who don’t like the way he does it. That’s pretty understandable, it seems to me, even if you’re a strong Republican.”