A critical House special election on Tuesday could provide some of the biggest clues yet about how much trouble Republicans could be in this November.
In Ohio, the last Republican vs. Democrat matchup before November has become the latest proxy fight for whether Democrats can harness the energy, activism and over-performance in past special elections to pull off an upset in a GOP-held district.
Republicans, meanwhile, have brought in President Trump himself and millions of dollars to stop that from happening, which would further trigger alarm bells about a possible blue wave in the fall midterms.
Four other states are holding their regular primaries — Kansas, Michigan, Missouri and Washington — where there are important House, Senate and gubernatorial contests on the ballot.
Several races feature some of the progressive vs. establishment battles that have divided the Democratic Party so far this year, and there are also more women running who could add to historic numbers.
On the GOP side, in addition to the House special election, President Trump has waded into competitive primaries as well — a further test of his considerable ability to sway his base for or against candidates, even though some national Republicans fear he could be boosting weaker candidates.
Here's what to watch on Tuesday night:
Ohio 12th special election: Canary in the coal mine for Republicans?
The Columbus suburbs, where Republican state Sen. Troy Balderson and Democrat Danny O'Connor are facing off, have a lot of the hallmarks that have proven problematic for Republicans in other recent elections — it's relatively affluent and highly-educated, Democratic turnout has been heavy in early voting, and it's not exactly hardcore Trump Country.
The GOP has struggled in special elections since 2016, and losses in Pennsylvania and Alabama have already added to their midterm worries.
A win by O'Connor in the seat vacated by former GOP Rep. Pat Tiberi could be the canary in the coal mine for Republicans. Ohio Republican Gov. John Kasich — who once held this seat in Congress — said Sunday on ABC's This Week the fact that the race has become a nail-biter should worry the GOP.
"The chaos that seems to surround Donald Trump has unnerved a lot of people. So suburban women in particular here are the ones that are really turned off... It really doesn't bode well for the Republican Party because this shouldn't even be close," Kasich said.
According to the Columbus Dispatch, through last week Democrats had returned absentee ballots in the district's most populous counties at a pace that nearly doubled that of Republicans. Comparatively, in the 2016 general election, GOP ballots outnumbered Democratic ballots by 9 percent.
Republicans, meanwhile, have poured millions into the race in the eleventh hour to save Balderson, falling back on one of their tried and true messages — stoking fears of a would-be Speaker Nancy Pelosi and rising progressivism within the Democratic Party. O'Connor has said he wouldn't support Pelosi as Democratic leader, though he did stumble on that question in an MSNBC interview.
O'Connor, the Franklin County recorder, hasn't made his message so much about Trump, but has zeroed in on health care, economic issues and comments Balderson made suggesting he might support raising the age of eligibility for Social Security and Medicare.
Trump held a rally for Balderson this past weekend, which Republicans hope will fire up base voters and drive up primary day turnout to counter any Democratic surge. But it could also have unintended consequences by turning off independents and moderate Republicans who don't like the president. The night before the rally, Trump also went off on Ohio favorite son LeBron James, the NBA player who just opened up a school for at-risk kids in his hometown of Akron.
Democratic primaries: Can progressives pull off more upsets?
The last big primary day at the end of June brought the upset victory by Alexandria Ocasio-Cortez over longtime New York Rep. Joe Crowley, the No. 4 ranking Democrat in the House. Now, in a handful of primaries on the ballot Tuesday, progressives are hoping they can re-create that magic, often with the help of their new 28-year-old heroine.
Ocasio-Cortez and Vermont independent Sen. Bernie Sanders rallied last month for two Kansas House candidates — Brent Welder in the 3rd District and James Thompson in the 4th District — who support progressive priorities like Medicare for all and a higher minimum wage.
Welder is vying to take on GOP Rep. Kevin Yoder in a top-targeted Kansas City suburban district, which Hillary Clinton won by 1 percent in 2016, and some national Democrats worry a far-left candidate could jeopardize their chances. EMILY's List has endorsed Sharice Davids, a former White House fellow under President Obama who would be the first openly lesbian Native American in Congress if she's elected. A third top-tier candidate, teacher Tom Niermann, has argued for a more centrist approach in trying to flip the district.
There's a similar dynamic happening in Michigan's 11th District, another top Democratic pickup opportunity in suburban Detroit. Ocasio-Cortez is backing Fayrouz Saad, a former Homeland Security official who would be the first Muslim woman elected to Congress. Hillary Clinton has endorsed Haley Stevens, who worked on the auto industry bailout under Obama. She has gotten union support, as has former state House Minority Leader Tim Greimel. Suneel Gupta, a health care technology executive and brother of CNN's Sanjay Gupta, is also running.
Ocasio-Cortez has also weighed in for Cori Bush, a young female challenger to Rep. William Lacy Clay in Missouri, hoping to provoke the kind of upset she was able to carry out against another Democratic stalwart. Bush is a pastor and civil right activist, while Clay has represented the district for almost two decades, succeeding his father who helped found the Congressional Black Caucus.
There's a divide in the Michigan gubernatorial primary too, where Democrats hope to pick up the seat of retiring Republican Gov. Rick Snyder. Long seen as the frontrunner, state Senate Minority Leader Gretchen Whitmer has gotten key labor endorsements and is backed by EMILY's List. She faces Dr. Abdul El-Sayed, who has the blessing of both Ocasio-Cortez and Sanders, and self-funding businessman Shri Thanedar.
Republican primaries: Trump endorsement could hurt general election chances in Kansas
Trump has also waded into several of Tuesday's GOP contests — much to the chagrin of some national Republicans.
The most noteworthy is in the Kansas governor's race, where Tuesday morning the president tweeted his support for Secretary of State Kris Kobach. He's a Trump ally who's been a conservative lightning rod on issues like immigration. He spearheaded Trump's efforts to prove widespread voter fraud in the 2016 elections — allegations still without proof.
The AP reported Trump weighed in against the urging of his aides, fearing a Kobach victory could endanger the GOP's hold on the state. Kobach is challenging incumbent GOP Gov. Jeff Colyer, who became governor after Trump chose Sam Brownback to be the U.S. ambassador-at-large for international religious freedom.
Trump also endorsed Michigan Attorney General Bill Schuette in the governor's race over Lt. Gov. Brian Calley, who withdrew his support for Trump in October 2016 in the wake of the infamous Access Hollywood tape. Snyder has backed Calley, though polls have shown Trump is more popular with Michigan Republicans than the outgoing governor.
In the Senate GOP primary for the nod to face Democratic Sen. Debbie Stabenow, Trump backed Iraq War veteran John James, who also has support from many in the GOP establishment. But James first has to fend off wealthy venture capitalist Sandy Pensler, who's poured millions into his own campaign.