By William Cummings, USA Today–

One of the most hyped and breathlessly awaited midterm elections in American history is upon us.

In the Senate, Republicans hold only a 51-49 majority, but the Democrats’ chances to flip control there are much slimmer because only nine of the 35 seats on the ballot this election were in Republican hands. And a number of the Democratic senators up for re-election are running in states that Donald Trump won comfortably.

Democrats will need to gain 23 seats to gain a majority in the House. History and the polls are on their side heading into Tuesday. For all midterm elections since the end of World War II, the president’s party has lost an average of 25 seats in the House, according to Gallup. That number jumps to 37 seats for presidents with approval ratings below 50 percent.

Here are the things to watch for on Election Day as the country waits to see whether the predicted “blue wave” for Democrats plays out.

Voter turnout

The party that gets the most of its voters to the voting booth will be the one that wins the close races and congressional control.

Polls have indicated that voters on both sides are a lot more fired up for this election than most midterms, when turnout is typically much lower than years when the president is on the ballot. For example, only 38.5 percent of voters turned out to vote in the 2014 midterms, according to the U.S. Census, compared with 56 percent in the 2016 presidential election.

Some believe that Republicans generally have a turnout advantage in midterm elections. While GOP turnout was higher in the last two midterms (2010 and 2014), an analysis by FiveThrityEight found since 1978 their advantage tends to evaporate when a Republican is in the White House.

A poll Sunday from ABC News and The Washington Post found that 80 percent of registered voters are “certain to vote” or have already voted, compared with 65 percent in 2014 and 71 percent in 2010.

Female voters

A key for Democrats will be the turnout of various demographic groups and one of the biggest will be female voters.

Trump’s presidency has fueled a resurgent gender war. From his defeat of the first female major party nominee for president to his own alleged sexual misconduct, Trump has outraged many women with his language, behavior and policies. The massive Women’s March on Washington after Trump’s inauguration and the rising number of women running for office are often cited as evidence of the extent that Trump has politically energized that voting bloc.

While women did not turn out in 2016 for Hillary Clinton the way Democrats might have hoped (Barack Obama actually won more of them as a percentage in 2008 and 2012), the majority of them have consistently voted Democrat in recent elections. If they vote in large numbers Tuesday, that could be enough to flip control of the House.

Young voters

Another group Democrats are counting on and could determine the election outcome is America’s youth.

A poll last month from the Harvard Kennedy School Institute of Politics found that just 26 percent of voters age 18-29 approve of the job Trump has done as president. Fifty-five percent said they would like to see a Democratic majority in Congress (and that number jumps to 66 percent of likely voters in that age range).

And there are a lot of them. Millennial and Generation X voters now outnumber their more senior cohorts, according to the Pew Research Center.

But they aren’t the most reliable voters. In the 2014 midterms, voters from the younger generations made up 53 percent of eligible voters but cast 21 million fewer votes than members of the older ones. A recent NBC News/GenForward survey found that only 31 percent of Millennial voters said they will “definitely vote,” while another 26 percent said they “probably” will.

African-American voters

There were many factors that led to Trump’s victory over Clinton, but a decline in African-American turnout was a big one. After voting in higher than normal numbers in races where Obama was on the ballot, those numbers receded in 2016.

Some polls have indicated that Trump has made gains among black voters, but even the rosiest projections for the president would still mean massive opposition from African-Americans.

Trump has been accused of racism by his critics and of sending “dog whistles” of solidarity to white supremacists. If those dog whistles backfire and draw African-American voters to the polls, they could carry a number of Democrats in close races –such as Stacey Abrams in Georgia’s gubernatorial race – to victory.

Latino voters

Latinos are more energized than in past midterm elections. According to Pew, 55 percent of registered Latinos are enthusiastic about voting in this election, compared with 37 percent in the 2014 midterm. And 63 percent said in a September survey that they would vote for the Democratic candidate for Congress.

But turnout in 2014 was a record low for Latinos and Trump’s rhetoric against Latino immigrants did not translate into a surge in 2016: 47.6 percent of Latinos voted in 2016, according to the Census, less than in 2012 or 2008.

Eastern House races

Of the 50 congressional districts currently considered toss-ups by the Cook Political Report, 17 of them are on Eastern Standard Time. Keep on eye those. If they all start breaking for Republicans, that could be a sign that the predicted Democratic wave isn’t coming. If they all start turning blue, there is a good chance that trend will continue as the polls close in the West.

The Trump factor

Although Trump isn’t on the ballot, many people, including the president, have cast the election as a referendum on his first two years as president. As noted earlier, a president’s popularity is often the determining factor in how a party performs in midterm elections.

And, as pundits constantly point out, Trump is no ordinary president. His inflammatory political style is a large part of why turnout is expected to be extremely high. A recent NBC News/Wall Street Journal poll found that 72 percent of voters plan to vote to send a signal of opposition (40 percent) or support (32 percent) to the president.

The Kavanaugh effect

Supreme Court Justice Brett Kavanaugh’s contentious confirmation process is being hailed by both sides as an important factor in the election.

After Kavanaugh was confirmed despite the allegations of sexual misconduct that nearly derailed him, Senate Majority Leader Mitch McConnell, R-Ky., said the Democrats’ tactics against him had the Republican base “fired up.” He said Republicans had defended due process while liberals had behaved as a mob.

Conservative radio host Hugh Hewitt said on Meet the Press that “on Wednesday, everyone’s going to be talking about Brett Kavanaugh.”

But many Democrats believe that amid the #MeToo movement, women were outraged and further energized by Kavanaugh’s confirmation. An Oct. 24 USA TODAY/Suffolk University poll found that 35 percent of respondents said Kavanaugh’s confirmation made them more likely to vote for a Democratic congressional candidate, while 27 percent said it made them more likely to vote for a Republican.