The topsy-turvy campaign, a referendum on the Democratic leader but also a crucial test of his predecessor Donald Trump’s continued sway in American politics, has seen Republicans on the offensive for much of the year.

The White House was emboldened by a summer backlash against efforts to restrict abortion, but soaring violent crime and stubbornly high inflation have pierced the consensus about a Democratic comeback.

US voters decide every two years who gets the majority in both chambers of Congress, and whether the president will get any new policies passed or if the opposition will be able to thwart his agenda.

All 435 seats in the House of Representatives are on the ballot on Nov. 8, as well as 35 Senate seats, just over a third of the upper chamber.

“We just have 15 days until one of the most important elections in our lifetime,” an upbeat Biden told activists on Monday at his party’s headquarters in Washington, D.C., predicting a late surge for the Democrats.

“And it’s going to shape the way the country looks [...] for the coming decade.”

The party of the sitting president typically loses two dozen House members and a handful of senators in the midterm elections, with its supporters less motivated to turn out.

After being down in the generic congressional ballot throughout August and September, Republicans now find themselves tied or with a slight lead in most polls.

The Cook Political Report has 192 House seats in its “lean”, “likely” or “solid” Democratic columns and 211 in those columns for the Republicans. The finishing line for majority control is 218 seats, meaning the 32 remaining “toss-up” races are where the rubber meets the road.

Divided Congress

The conventional wisdom is that Republicans will prize back the House from the Democrats with a possible gain of around 20 seats. That would enable them to fulfill promises of extensive investigations, including potential impeachment proceedings, against Biden and his administration.

The evenly divided Senate, currently controlled by the Democrats thanks to Vice President Kamala Harris’s tie-breaking vote, will be more of a toss-up.

The RealClearPolitics polling average has Nevada as the closest race, followed by Georgia, Pennsylvania, Ohio and then Arizona. But polling leads in all of these races suggest photo finishes on Election Day.

“Why so many people offer such confident predictions about the Senate continues to baffle me,” Cook Political Report founder Charlie Cook said in a recent commentary, arguing that an unchanged 50-50 chamber remained “possibly” the most likely outcome.

A divided Congress would prove a slog for Biden as he attempts to cement the legacy of a single term or make the case that he should be reelected in 2024.

Beyond regular set pieces such as government funding votes, little legislation would be possible with a Republican House and Democratic Senate at loggerheads.

Biggest headache

Governors’ mansions are also on the ballot in dozens of states, as well as elections for the secretaries of state and attorneys general seen as crucial to ensuring free and fair elections.

Pro-democracy activists have voiced concerns over the high number of Trump-backed candidates running on a platform of denying that Biden won the last election fairly.

Strategists in both parties acknowledge that reproductive rights animated Democratic supporters like no other issue in the summer, after the Supreme Court gutted federal protections for access to abortion.

But Democrats fear the public outrage peaked too soon and the issue has fallen behind the economy, crime, immigration and threats to democracy among voters’ stated priorities.

Democrats are instead banking on getting credit for the White House finally clinching legislation on boosting domestic manufacturing, tackling climate change and lowering prescription drug prices.

And they will be hoping to reassemble the anti-Trump coalitions that swept them to victory in the House in 2018 and the White House in 2020.

The Republican leader remains his party’s biggest headache, both for his high-profile legal troubles and his backing of extremist candidates who have struggled in close contests the party was expected to win easily.

“The fake polls and so-called ‘experts’ are telling us that we will fail at winning back our Republican majority in the Senate,” Trump said in a fundraising email on Sunday.

“They were wrong in 2016, and they’re wrong now.”