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How powerful would President Hillary Clinton be?

The Democrats will likely retain the White House, but taking over Congress is a taller order.

By jonathan Jones

Hillary Clinton will probably be the next President of the United States. She is certain to be the Democratic nominee, and her Republican opponent will be the deeply unpopular Donald Trump. Betting markets give Clinton a 72% chance of winning both the primary and the general election. But even if the Democrats retain the White House, how much they’re able to get done will depend largely on whether they’re also able to take back control of Congress.

Yes, it’s not just the presidency that’s at stake in November. All 435 seats in the House of Representatives and 34 of the 100 in the Senate are up for election too. The Republicans currently have majorities in both chambers. Can the Democrats change that in November?

To gain a majority in the House of Representatives, the Democrats would have to win 218 seats – 30 more than they managed in 2014. Democrats should expect to make at least some gains: they tend to do better in presidential election years than midterms (benefiting from higher turnout), and the Democratic Party’s popularity has increased slightly since the 2014 elections while the Republican Party’s has worsened considerably.

But 30 seats is a lot to make up in one go – especially as there are only 16 seats that Democrats lost by less than ten points in 2014. To gain 30 seats on a uniform swing would require a 16-point swing from the Republicans to the Democrats – which would mean them winning around 53.5% of the national popular vote. (They won 45.6% in 2014.)

That is possible. The Democrats won 54% of the popular vote in house races in 2008, when they were helped by a very popular Democratic presidential nominee in Barack Obama and a very unpopular outgoing Republican President in George W. Bush.

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However, elections in 435 individual districts don’t swing uniformly, and even if the Democrats can manage a repeat of their 2008 national vote share – helped by Trump’s unpopularity at the top of the Republican ticket – they may not gain the 30 seats they need.

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That’s because, of the 30 seats that saw the narrowest Republican victories in 2014, 22 are ones Republicans won from Democrats, giving them an incumbency bonus this year that they didn’t have then. In ten of them, the Democrats had the benefit of an incumbent running in 2014, but obviously won’t this time.

So taking back the House will be tough for the Democrats: forecasters give them just a 23% chance and PredictWise just 12%. But they have a much better chance when it comes to the Senate.

Democrats need a net gain of four seats to regain control of the upper chamber (assuming there’s a Democratic President and therefore a Democratic Vice President to break any ties as President of the Senate; otherwise they need five). There are seven very competitive races: six Republican seats in states won by President Obama in 2008 and 2012 (Florida, Illinois, New Hampshire, Ohio, Pennsylvania and Wisconsin) plus the Democratic-held seat in Nevada, where Senate Minority Leader Harry Reid is retiring. Democrats probably need to win at least five of these seven to take control of the Senate.

In four of those races, Democrats have given themselves a strong start by recruiting candidates who have previously won state-wide election to high office: former Attorney General Catherine Cortez Masto in Nevada; Governor Maggie Hassan in New Hampshire; former Governor Ted Strickland in Ohio, and former Senator Russ Feingold in Wisconsin.

In Illinois, Iraq War veteran and two-term Congresswoman Tammy Duckworth is worrying Republican incumbent Mark Kirk to the point that he felt the need to release an internal poll showing him three points behind. Last month, Pennsylvania’s Democratic voters chose Katie McGinty – who’d been endorsed by Barack Obama, Joe Biden and the Democratic Senatorial Campaign Committee ­­– to be their nominee over the party’s losing candidate in 2010, Joe Sestak. In Florida, neither party has selected its candidate to replace Marco Rubio, who eschewed a re-election bid in favour of his ill-fated presidential campaign.

Overall, Democrats are the favourites to control the Senate from January 2017: forecasters give them a 60% chance, and betting markets a 64% one. But with Republicans favoured to retain the House, US politics is likely to continue its latest period of divided government that began when Democrats lost control of the House in the 2010 midterms.