Updated at 1:23 p.m. ET

Tuesday's Illinois primaries could bring down the first congressional incumbent of 2018, set the stage for a highly competitive gubernatorial race, and give Democrats challengers against several possibly vulnerable GOP congressmen they're aiming to defeat in order to take back the House.

There are also big signs of Democratic enthusiasm, both in how many candidates are running and in the donations voters are willing to make.

The biggest race to watch on Tuesday offers further clues into discordant wings of the Democratic Party — the battle between Rep. Dan Lipinski and progressive activist Marie Newman, who's challenging the centrist incumbent from the left.

Republican Gov. Bruce Rauner also faces a primary challenge from a right-wing activist. Even if he survives the primary, Rauner is probably the most endangered GOP gubernatorial incumbent in the country, and Democrats will soon know which candidate will take him on after settling their own expensive party contest.

And as Democrats eye the 23 seats they need to take back the House, there are several districts in Illinois that could be essential paths to that goal. Tuesdsay's votes will decide which candidates try and oust GOP incumbents.

Here are the races to keep an eye on once polls close at 8 p.m. ET.

House primaries to watch: Will the Democrats' path to the majority run through Illinois?

There are four GOP House seats in Illinois which could be in play come November. Democrats have seen a surge in fundraising and in candidates running across the state so far — just some of the potential signs that could portend a blue wave. But first, who emerges from the Democratic primary could have big implications on how competitive each race will be.

The Cook Political Report rates the contests against Rep. Peter Roskam in the 6th Congressional District and Mike Bost in the southwest Illinois 12th Congressional District as toss-ups.

Roskam's suburban Chicago district is one of 23 Republican districts that voted for Hillary Clinton in 2016, and this could be his toughest race since winning the seat in 2006. Financial adviser Kelly Mazeski has spent the most of any candidate in the Democratic primary, and she's also been endorsed by EMILY's List. Amanda Howland, Roskam's 2016 opponent, is also running, along with scientist Sean Casten, Naperville City Councilwoman Becky Anderson Wilkins and Carole Cheney, a former aide to Illinois Rep. Bill Foster.

The next best target for Democrats is Bost's southwest district along the Missouri border, and after wooing him to jump in for several cycles, Democrats are excited about St. Clair County State's Attorney Brendan Kelly there, who's expected to have the edge over businessman David Bequette in the primary.

Trump won downstate areas like Bost's district and Rep. Rodney Davis' central Illinois district by appealing to white, working-class voters there, but Democrats believe these areas have soured on the president and they could have a shot at these seats. Davis' 13th Congressional District is rated Likely Republican by Cook, and the Democratic race there is seen as a contest between Illinois senior Sen. Dick Durbin's former fundraiser Betsy Dirksen Londrigan, who has the backing of her former boss and EMILY's List, and former Illinois assistant attorney general Erik Jones.

The 14th Congressional District, represented by GOP Rep. Randy Hultgren, which is rated Likely Republican by Cook could become a contest as well, though it's still a reach. The two top candidates there are former Health and Human Services official Lauren Underwood and engineer Matt Brolley, according to Roll Call.

Looking ahead to what could come in the fall, Democrats are putting the GOP on the defensive by running more candidates, including in safe GOP territory. They are also getting the lion's share of small-dollar donations to House candidates this year, a sign of voter enthusiasm.

Illinois 3rd District: Lipinski tries to hang on

Seven-term Rep. Dan Lipinski has never been a typical Democrat — he opposed the Affordable Care Act, has voted with President Trump on some immigration measures and is anti-abortion rights. Until now, the former political science professor breezed through to re-election in this southwest Chicago district he essentially inherited after his father, Bill Lipinski, retired from Congress in 2004.

But challenger Marie Newman has the backing of two Illinois incumbent members — Reps. Jan Schakowsky and Luis Gutierrez — and she could very well come out ahead on Tuesday night after a particularly nasty primary fight. Newman also has support from major liberal groups, such as Planned Parenthood, NARAL Pro-Choice, EMILY's List, MoveOn.org and the Human Rights Campaign.

Lipinski, a member of the centrist Blue Dog Coalition, declined to endorse former President Obama in his 2012 re-election campaign, and former top Obama aides such as David Axelrod have also weighed in for Newman. But Lipinski still has the backing of some top labor groups, and Democratic House leaders, including House Leader Nancy Pelosi and Democratic Whip Steny Hoyer, have all still stood behind the incumbent.

Meanwhile, some conservative and middle-of-the-road groups have tried to save Lipinski, with the anti-abortion rights group Susan B. Anthony List sending in canvassers, while the bipartisan group No Labels has been funding a superPAC to help him. This will be a safe Democratic seat in November, no matter which Democrat wins. Republicans have their own headache on the ballot — the only GOP candidate who filed to run is a white supremacist and former leader of the American Nazi Party.

Illinois governor: High spending affairs on both sides

Gov. Bruce Rauner would likely be the most endangered GOP incumbent in governors' races this fall, if he can first beat back a primary challenge from state Rep. Jeanne Ives, a staunch conservative who has received favorable coverage from Breitbart News. She's hit the incumbent as being too liberal, particularly on abortion after he signed a bill last fall to expand abortion coverage for women on Medicaid.

Rauner, the wealthy former venture capitalist, has already spent over $50 million of his own money. He had been figured to win comfortably, but there are reports of concern among Republicansin Illinois that the race could end up closer than expected.

As Politico noted, he's tried to woo different factions, first in the primary and then looking ahead to the general, which has caused him some headaches. The governor vetoed a gun store licensing bill. That could help him win over conservatives, but will surely come back to haunt him in November's election. The Democratic Governors Association, seeing Ives as the weaker candidate, has also tried to meddle in the primary, running ads calling the challenger "too conservative" but then listing off her anti-abortion and pro-gun credentials in hopes of motivating her supporters to go to the polls.

Polling has shown Rauner's approval ratings are even lower than President Trump's in the state, and last year the conservative National Review called him the " worst Republican governor in America." He also came under fire for how he handled a Legionnaires' disease outbreak at veterans facility in the state that killed 13 people.

The Democratic race has been pricey as well, with billionaire J.B. Pritzker already spending $70 million of his own money to secure the nomination — a new primary record. Pritzker's family founded the Hyatt hotel chain and he's the brother of former Obama Secretary of Commerce Penny Pritzker.

Pritzker's main rivals for the nomination — businessman Chris Kennedy, who's the son of Robert F. Kennedy, and state Sen. Daniel Biss — have slammed the front-runner for spending so heavily, in what's amounted to more than half a million dollars per day.

"It's being used to blot out the argument to buy up the airways so that the discourse doesn't occur," Kennedy told NBC Chicago. "I think people are sick of Mr. Pritzker's use of the airways to do that." Early polling showed Pritzker was the heavy favorite, but his advantage may have narrowed. He's come under fire over his family's use of offshore accounts to reportedly avoid taxes, and he's only released the first two pages of his personal returns. Pritzker also had to apologize after wiretaps of a 2008 conversation he had with disgraced former Gov. Rod Blagojevich revealed he made disparaging remarks about African-American politicians as they weighed who to appoint to finish the Senate term of Obama once he was elected president.

Those are just some of the issues Kennedy and Biss have seized upon to argue that Pritzker would jeopardize Democrats' shot to unseat Rauner. Still, Pritzker has the endorsement of both Illinois Sens. Tammy Duckworth and Dick Durbin and the backing of major labor groups. Biss has tried to claim the progressive mantle in the race, and Our Revolution Illinois, which evolved from the presidential campaign of Sen. Bernie Sanders, I-Vt., has endorsed him.

Illinois 4th District: Who will succeed Gutierrez?

The three-way race to replace retiring Democratic Rep. Luis Gutierrez in this Latino majority district is between two candidates — Cook County Commissioner Jesus "Chuy" Garcia, who has the blessing of the outgoing congressman, and nonprofit executive Sol Flores, who is being backed by EMILY's List. Chicago police officer Richard Gonzalez is also running.

Garcia is probably the front-runner for the nomination, and he has plenty of name ID after unsuccessfully challenging Chicago Mayor Rahm Emanuel in 2015. He was eyeing another bid next year, but after Gutierrez made his announcement, Garcia shifted his focus to Congress instead. He's tried to claim the progressive mantle in the race, and Sanders held a rally last month on his behalf.

Flores is a former management consultant who left to found La Casa Norte, a group which just broke ground on a $20 million facility that will include a community health center and affordable housing. She's criticized Gutierrez for trying to anoint his successor, calling it an "old-school move" to the Chicago Sun-Times.

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