Four Democrats who could challenge Gov. Bruce Rauner in 2018

Republican Gov. Bruce Rauner sent two clear signals when he dumped $50 million into his campaign fund: The 2018 race for Illinois governor will be a rough one, and the contest starts now.

What's still unknown is which Democrats will try to unseat the multimillionaire former businessman. Among those contemplating a bid are U.S. Rep. Cheri Bustos, businessman Chris Kennedy, state Sen. Andy Manar and billionaire investor J.B. Pritzker, according to potential candidates and aides.

In a glimpse of what's to come, the Democratic Governors Association said Rauner is "more focused on getting elected than passing a budget or growing Illinois' economy," and that his cash infusion "won't make Illinois voters forget about his past 2 years of failure."

Illinois Republican Party spokesman Steven Yaffe fired back that the election will "present a clear choice between those like Gov. Rauner who want to reform state government so it works for the taxpayers and those who will simply raise taxes without reforming the status quo in order to protect the political insiders and special interests."

Here's a look at some of the Democrats who could challenge Rauner:

U.S. Rep. Cheri Bustos

Bustos is a Springfield native and former member of the East Moline City Council. She was first elected in 2012 to represent the 17th Congressional District, which comprises a swath of western and northern Illinois.

A senior adviser to Bustos said many people have urged her to consider running since she won re-election last month by a 20-point margin in a district that voted for Republican Donald Trump.

Bustos is "giving it serious consideration," adviser Stacy Raker said. "Cheri thinks Bruce Rauner has been an absolute disaster for working families in her district and across our state, so she's committed to making sure Democrats have a candidate who can defeat him in 2018."

Chris Kennedy

His is a name with a political legacy, as he's the son of the late Robert and Ethel Kennedy.

The former chairman of the University of Illinois Board of Trustees, Kennedy runs a grocery nonprofit, Top Box Foods.

He appears to be the closest to launching a bid, though he has flirted with running for office in the past and not followed through. He has been hiring campaign staff and an announcement is expected in January, according to an adviser who spoke on condition of anonymity because an official campaign staff has not been assembled.

Kennedy has been traveling the state and meeting with party leaders such as House Speaker Michael Madigan, who leads the Democratic Party of Illinois, saying Kennedy would be an "excellent candidate."

State Sen. Andy Manar

The former chief of staff to Senate President John Cullerton said he's giving a bid "serious consideration." He's been meeting with party leaders, supporters and potential donors but said he doesn't have a timeline for an expected decision.

Manar was first elected in 2012, and has been heavily involved in efforts to reform Illinois' school funding formula.

He said the gridlock that's occurred since Rauner took office has been "devastating." Lawmakers have been unable to pass a budget, leading to multibillion-dollar bill backlogs and deep cuts to social services and other areas.

"One way or another I'm going to be part of crafting a strategy so that (Democrats) win elections in 2018,"Manar said.

J.B. Pritzker

Pritzker is a billionaire businessman and philanthropist who has the bank account to compete with the governor's own personal wealth, and a spokesman said he would be willing to use it.

The spokesman declined to be identified because he has typically represented Pritzker in business, not political, matters.

Pritzker also has proved fundraising skills, raising millions for Democratic presidential candidate Hillary Clinton.

The spokesman said the venture capitalist and entrepreneur is motivated by the damage he's seeing to things he cares about, such as social services and economic development. He said Pritzker is "very seriously considering" a run, but a decision isn't imminent.