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The 2018 U.S. congressional midterm elections are about one thing: the Presidency of Donald Trump.

While Trump himself won’t be on the ballot, Americans will look back on the last two years under the Republican president and decide how the next two years will be shaped.

Will the grasp of the GOP – currently in control of both the House and the Senate – remain or will a “blue wave” of Democrats shut down Trump’s agenda for his remaining time in office?

Here’s everything you need to know about what Americans will vote on, key races to watch, and what the outcome could mean for each party and why Canadians should care.

What are the midterms exactly and what are people voting on?

This March 5, 2018, file photo shows the East Front of the U.S. Capitol at sunset in Washington. AP Photo/Alex Brandon, File

Scheduled to take place on Nov. 6, the midterm elections are part of a system of checks on the U.S. political system and presidency.

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House members serve two-year terms meaning the contests happen along with presidential elections and in “off years” without a presidential race, like 2018. The staggering of the elections means that either a presidential or a midterm election is held every two years.

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Americans will vote on all 435 seats in the House of Representatives. In the Senate, just 35 of the 100 seats in the Senate, will be in play this year as Senators serve six-year terms.

At the state level, 39 state and territorial governorships will be up for grabs and voters will also decide a number of ballot measures on issues ranging from abortion, voter ID laws, Medicaid health insurance and marijuana.

University of Toronto political science professor Ryan Hurl said midterm elections are one way of regularly going back to the people to re-assess the state of power.

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“You’re going to have different assessments of public opinion in a president’s term,” Hurl said. “It’s much more difficult for a president to maintain an agenda if that agenda – in practice – is not supported by a majority of the populations.” Tweet This

Who is in control of Congress?

Republican lawmakers applaud as President Donald Trump speaks to a joint session of Congress on Capitol Hill in Washington, Feb. 28, 2017. AP Photo/J. Scott Applewhite

Currently, Republicans control both levers of powers in Congress, with Democrats trying to win back the House, and possibly, the Senate.

The Democrats have 193 seats to Republicans’ 236 with six vacancies.

The Dems will need a net gain of roughly 25 seats to win a 218-member majority in the 435-seat chamber. A statistical analysis from FiveThirtyEight shows the Democratic Party winning a slight majority.

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The website gave the Democrats a roughly 82 per cent chance of winning the House.

Winning the Senate will be a much more difficult task for Democrats. The GOP hold 51 of the 100 seats, but the Senate races will be especially tough for the Dems who are defending 26 of the 35 seats being contested.

Republicans have a 66 per cent chance of winning the Senate, according to FiveThirtyEight.

The odds for Republicans are also in their favour as 10 of the 26 incumbent Democrats are in states Trump won in 2016.

What is at stake for the Dems and GOP?

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A win for Republicans could mean further dismantling Obamacare and appointing more conservative judges to courtrooms.

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If Democrats win control of either chamber, Trump’s legislative agenda would be mostly dead on arrival, meaning no border wall, no cuts to welfare and social security, and no further tax cuts.

It could also lead to a re-examination of immigration reform, including revisiting the Obama-era Deferred Action for Childhood Arrivals (DACA) policy that shielded young people from deportation who came to the U.S. illegally with their parents.

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Geoffrey Skelley, a political analyst at the University of Virginia Centre For Politics, said if Democrats win, it would create a gridlocked Congress stymieing Republicans. It would also give Dems subpena power, allowing them to investigate the president far more aggressively on issues like Russian collusion.

“They are going to be able to set up select committees on the investigation into the Trump administration,” he said. “This is worrying for the Trump administration.”

House and Senate committees can send subpoenas for documents and can compel witnesses to testify under oath.

Blue wave or red wave coming?

Every day, there seems to be a new story or scandal that could change what happens between now and November.

Generally, it’s believed that the Senate is likely to stay Republican, while Democrats have a strong chance to win the House, anywhere from between 50 to 77 per cent, leading many to predict a “blue wave” is coming in November.

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Democrats have consistently won state-level elections and special elections, managing to flip 11 seats in Congress this year to the Republicans’ two.

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Meanwhile, Trump has long predicted a “red wave” of Republican victories and warned that any GOP losses could threaten public safety and weaken the nation’s borders.

Trump and Republicans will campaign on the booming economy, which added about 200,000 new jobs in August and saw the unemployment rate drop to an 18-year low.

And while there is little evidence of a “red wave” at the polls, Hurl said it’s important to remember there was little indication Donald Trump would win in 2016.

“A party that doesn’t control the presidency tends to do well,” he said. “It is possible, again, that all the polls are off in a similar direction. And that, for whatever reason, they’re not capturing a radical change in American public sentiment.”

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What is at stake for Donald Trump?

President Donald Trump sits with Attorney General Jeff Sessions during the FBI National Academy graduation ceremony, Friday, Dec. 15, 2017, in Quantico, Va. AP Photo/Evan Vucci

Historically, the president’s party does not do well during midterm elections.

Barack Obama’s Democrats lost 63 House seats during the first midterm in 2010 and during George W. Bush’s second term, the GOP lost 30 seats.

Trump’s approval rating has risen slightly since the fall of 2017 but remains at 43 per cent, according to the RealClearPolitics average. Obama’s was 45 per cent before the 2010 midterms that led to a Republican landslide.

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Skelley said the 2018 midterms would be game-changing for Trump’s presidency: one way or another.

“Midterms are usually a referendum on the president,” Skelley said. “Trump is far away, the No. 1 issue in this election.”

In addition to hampering Trump’s agenda, if the Democrats win the House, the 25th amendment could be in play. The Dems could potentially vote to impeach Trump, although it would be virtually impossible as they would need two-thirds of the Senate.

What are the key House and Senate races?

A man marks his ballot at the Santa Monica City Hall polling station as Californians go to the polls in California’s primary election in Santa Monica, Calif., on June 5, 2018. California is a heavily Democratic state and Democratic Party leaders hope to flip a number of congressional seats in November’s midterm elections. EPA/MIKE NELSON

The non-partisan Cook Political Report rates 66 of the 435 House races as competitive as of Sept. 9. Of those, 30 are considered “toss-ups” that could go either way.

California has the highest number of these districts, with seven — Democratic-leaning states such as Virginia, New Jersey, Washington and Colorado are also listed as competitive.

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Meanwhile, the key battlegrounds for the Senate are: Nevada, Arizona, Tennessee, Indiana, Missouri, Montana, West Virginia, and North Dakota.

“The House is the main focus because it has the most potential for seeing divided government become a reality,” Skelley said. “The Senate is more likely than not going to remain in Republican hands.”

However, Senate Majority Leader Mitch McConnell, R-Ky., said earlier this week that the Senate races are “too close to call,” comparing them to “a knife fight in an alley.”

“All of them too close to call and every one of them is like a knife fight in an alley,” he said. “It’s just a brawl in every one of those places.” Tweet This

Why should Canadians care?

Donald Trump meets Justin Trudeau at the Welcome Ceremony at the G7 summit in Charlevoix. EPA/NEIL HALL

Canada is not going to the front and centre of the elections but there are still many reasons why Canadians should follow closely.

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Amid tense, ongoing NAFTA negotiations between the two countries and severe tariffs imposed by the Trump administration, there is plenty at stake economically.

READ MORE: Auto tariffs would be ‘devastating’ for both Canada and U.S.

And with the midterms less than eight weeks away, Trump is facing pressure to maintain the Republican hold on the House and Senate as it could influence trade talks. The approval of Congress is necessary to rewrite any trade deal and a Democratic House could refuse to endorse an agreement that excludes Canada.

“A Democratic House would push Trump to adopt a more conciliatory trade policy but that is very much uncertain,” says Hurl.

What Canadians should also watch for is whether 2016 was an aberration or if the U.S. under Trump has truly shifted towards nationalism and populism.

“How deep is that in the United States? Was 2016 the last blip of this or have the political alliances been shuffled in unusual ways?” he said. “It’s going to clear up a lot about where the United States is heading.”