Washington (CNN) Voters are now 100 days away from delivering their verdict on President Donald Trump's first two years in office, and while the political landscape could shift dramatically in three months, right now, the wind is at Democrats' backs.

Democrats need a net gain of 23 seats to wrest control of the House away from Republicans. And they need a net gain of two seats to take a Senate majority, although the path to get to that number is difficult.

Trump got some welcome news on Friday, with the announcement that the economy grew at a 4.1% in the second quarter, the best number since 2014. Trump will surely make that growth part of his midterms pitch to voters.

But despite a strong economy, the GOP's woes are evident in Trump's sagging approval rating and Democrats' edge in the generic congressional ballot. They're even more stark with Democratic candidates outraising Republicans in the vast majority of competitive races.

But the biggest problem for the GOP -- which has played out consistently in special elections over the last year -- is that Democratic voters are much more enthusiastic, and therefore more likely to vote in November.

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It has left Republicans split: Some are banking on Trump's appeal to turn out their base, while others are seeking ways to distance themselves from a President who is unpopular with moderate and independent voters and has sparked a ferocious backlash on the left.

Trump hails the announcement that the US economy grew at a 4.1% in the second quarter.

Trump has urged Republicans to focus on base issues, like immigration, which the President has hammered Democrats on for much of the year, accusing them of wanting open borders and encouraging gang violence. Democrats are laser focused on attacking the Republican health care bill and attempts to repeal Obamacare, two positions unpopular with moderate voters.

Here are five key themes to watch over the next 100 days:

Democratic performance in special elections

Democrats are fired up.

A recent study from Pew Research found turnout -- particularly on the Democratic side -- has been up considerably in primaries. According to Pew, the total number of votes cast in Democratic primaries is up 84% from this point in 2014.

Yes, some of that is because there have been more contested primaries, which increases turnout. But that excitement has also extended to a series of special elections. Democrat Conor Lamb won earlier this year in suburban Pittsburgh in a district Trump won by 20 points.

Democrat Conor Lamb won in a district Trump took comfortably.

Democrat Hiral Tipirneni came within a few points of turning blue a reliably red district in suburban Phoenix, Arizona.

The result, coupled with Lamb's win and other strong Democratic special election performances, worried Republicans.

"This was not supposed to be this close," a senior Republican said when the results came in. "We really can't blame anything. We got killed among independents. It shouldn't have been this close."

Democrats have also won on the local level, too, using special elections to flip 43 seats in different state legislatures since Trump stepped into the White House.

The next test will come in suburban Columbus, where Democrat Danny O'Connor is looking for a Lamb-like performance next month over Republican Troy Balderson to flip the reliably red district.

The year of the woman

Women are the most dominant force in Democratic politics -- one that crosses age, ethnic and ideological lines.

The fury of the Women's March the day after Trump's inauguration has led to record numbers of female candidates. And in competitive primaries, women are winning.

Alexandra Ocasio-Cortez is trying to put a leftist stamp on the Democratic class of 2018.

Among the stunners: Progressive Kara Eastman beat former Rep. Brad Ashford in a House primary in Nebraska; Alexandria Ocasio-Cortez ousted the No. 4 House Democrat, Rep. Joe Crowley, in New York; and Amy McGrath, a fighter pilot who bested Lexington Mayor Jim Gray, a top Democratic recruit, in a House primary in Kentucky.

Many of the winners have been backed by EMILY's List, which trains and funds female Democratic candidates for office.

But the trend goes much farther than who's on the ballot.

Women favor Democratic candidates for the House by a 25-point margin -- helping Democrats to a 12-point edge in the generic ballot, where those surveyed are asked whether they'd prefer a Democratic or Republican member of Congress to represent them, a Quinnipiac University poll out last week found.

The shift, most drastic in suburban areas, could be insurmountable for Republicans in some districts, much like the rise of rural voters helped catapult Trump to the White House two years ago.

Trump's tariffs beget Republican fears

That brings up another issue for Republicans: Those rural voters, though, may not be as rock solid in 2018.

Trump's plan to impose tariffs on countries he believes have treated the United States unfairly on trade has caused China, the European Union, Canada and Mexico to raise trade war fears and, in some cases, impose retaliatory tariffs. Those moves have shaken farms in Trump country, spreading fears that markets once seen as critical to soybean growers, pork producers and apple farmers -- to name a few -- are about to dry up.

The President and his supporters have looked to tamp down on concerns, arguing that short-term pain is worth the long-term gain.

But Republicans tasked with holding the House in 2018 have grown increasingly worried that trade fears could dampen otherwise good economic news.

The Republican Party still dominates rural America, and there is little on the Democratic horizon to break the hold, but the fear among Republican operatives is that voters who were once animated to stand with the President will stay home in November.

Eying a shot at Trump, Democratic presidential hopefuls test road message

Ask any Democrat considering a run at Trump in 2020 about their prospects and they will say they are focused on the midterms.

And that, to a degree, is true. The nearly two dozen Democrats rumored to be considering a presidential run have blanketed the country with endorsements, fundraisers and events, hoping their work impresses Democratic activists and wins favors from lawmakers they help elect.

But these Democrats, like Massachusetts Sen. Elizabeth Warren, Vermont Sen. Bernie Sanders and Vice President Joe Biden, to name just three, are also honing their messaging ahead of a possible run, using the midterms to road test their vision of the party they hope to lead.

"I don't talk about Clinton voters or Trump voters. I don't talk about white workers and black workers and Latino workers. I talk about workers and I talk about voters," Sen. Sherrod Brown, an Ohio Democrat, said of his party earlier this year.

Sanders, for example, has used his star power to endorse liberal candidates, some of whom are not backed by the Democratic establishment. California Sen. Kamala Harris, likewise, has focused on Democrats of color, and Biden has used his claim to the Obama mantle to back Democratic heavyweights and call more in his party to reach out to Trump voters.

Former Vice President Joe Biden has urged more in his party to reach out to Trump voters.

"The 2018 election will be a massive uphill climb," Warren said earlier this year. "And while we'd rather talk about great ideas, we can't climb that hill by ignoring the millions of Americans who are angry and scared about the damage this president and this Republican Party have done to our democracy. We can't ignore it, and we shouldn't want to ignore it."

There are post-2020 factors in November's midterms, too: 36 governor's offices are on the ballot this year, including 26 for states with Republican governors. Democrats hope to pick off several of those seats, which would in many states give them the power to veto gerrymandered congressional maps. It's a technical concern, but one with ramifications for control of Congress for the next decade.

Unsettled Senate map

The most uncertainty 100 days out from the midterms is over the Senate landscape -- where many of the most competitive states are largely rural and voted for Trump in 2016.

There are at least nine major battlegrounds -- with six pick-up opportunities for Republicans and three for Democrats.

The most vulnerable Democrats appear to be Sens. Heidi Heitkamp in North Dakota, Joe Donnelly in Indiana, Claire McCaskill in Missouri and Bill Nelson in Florida. Montana Sen. Jon Tester and West Virginia Sen. Joe Manchin also have tough races on their hands.

One thing most of those states have in common: They're rural, which means the fallout from Trump's trade wars is likely to hit farmers, who are largely-pro-Trump, first.

Another factor looming large in Senate races is the battle over the confirmation of Brett Kavanaugh to the Supreme Court. Republicans see a court fight as a way to energize a turned-off base -- but with the timing of a vote uncertain, it's not clear how potent an electoral issue it will be.

Democrats, meanwhile, are focused on ousting Republican Sen. Dean Heller in Nevada -- the only competitive Senate seat in a state Hillary Clinton won in 2016 -- and winning open-seat races in Arizona and Tennessee, where former Gov. Phil Bredesen's moderate message has so far helped him appeal to Republicans and independents.

One to watch: Texas, where Republican Sen. Ted Cruz faces a fundraising juggernaut in Rep. Beto O'Rourke. Polls have shown Cruz with a consistent lead, but O'Rourke raised more than $10 million largely through online, small-dollar donors in 2018's second quarter and will be able to afford what's sure to be a nasty campaign.