Wisconsin Republican Gov. Scott Walker speaks at the Republican National Committee summer meetings in Chicago, Friday, August 8, 2014. (AP Photo/Kamil Krzaczynski)

No discussion about the 2016 presidential campaign would be complete without Wisconsin Gov. Scott Walker (R). But that could change in just 12 weeks.

That's because Walker, a national conservative star, faces a tough reelection campaign. The general election officially kicked off for him Tuesday with ex-state commerce secretary Mary Burke's easy win in the Democratic primary.

No other potential 2016 hopeful has as much riding on the midterm election as Walker. If he wins on Nov. 4, he will be well-positioned to move toward a campaign for president as a hero of the right and a proven swing state victor. But a loss would vanquish him from the short list and mark the end of a tumultuous tenure as governor of one the country's most politically divided states.​

Burke faced only a token challenge in the Democratic primary. She defeated state Rep. Brett Hulsey by a wide margin.

In addition to Wisconsin, voters in Minnesota and Connecticut also went to the polls on Tuesday. Former ambassador to Ireland Tom Foley (R) advanced to a rematch against Connecticut Gov. Dan Malloy (D). Opinion polls conducted this year have shown the race is competitive.

In Minnesota, businessman Mike McFadden won the Republican primary for U.S. Senate. He will begin the general-election campaign as an underdog against Sen. Al Franken (D). Franken easily defeated his primary challenger. Hennepin County Commissioner Jeff Johnson (R) will face Gov. Mark Dayton (D), who is favored to win reelection. And 2010 gubernatorial nominee Tom Emmer won the GOP nomination for the seat of retiring  Rep. Michele Bachmann (R). He will face Sartell Mayor Joe Perske (D).

Polls show Walker has a real race on his hands against Burke. A recent Marquette Law School survey showed Walker (46 percent) and Burke (47 percent) in a dead heat.

Walker is also dealing with potential blowback from his alleged connection to a “criminal scheme” to coordinate the activities of conservative groups. A prosecutor has clarified through his attorney that Walker was not a target of the investigation. But in politics,  it's never a good thing to see the words "criminal scheme" mentioned in the same sentence as your name.

Burke, a former executive at the bicycle company Trek, has decided to center her campaign on the economy. Specifically, she is singling out Walker's unfulfilled promise to create 250,000 jobs by the end of his first term. Burke has already hit the airwaves with a commercial on the subject.

Walker rose to national prominence following his 2011 law to curb collective bargaining for public employees. Labor leaders and liberal allies revolted -- first with intense protests in Madison and later through pushing recall elections against Walker and Republican lawmakers who voted for his bill.

But conservatives -- both inside and outside Wisconsin -- rallied to Walker's side. He survived the backlash, and arguably emerged stronger. Walker won his 2012 recall election against Milwaukee Mayor Tom Barrett (D) by a wider margin than he defeated him in 2010.

The recall, Burke said in an interview last week, "enabled Walker to build a national fundraising base."

Walker's financial might is one reason why he should not be underestimated in the fall campaign. He outraised Burke more than 2-1 during the first half of the year.

The money enables Walker to try to negatively define Burke through TV commercials like a recent one that tied her to unpopular former governor Jim Doyle (D). Burke served as state commerce secretary under Doyle.

The Republican Governors Association has already started attacking Burke and is expected to spend big to help Walker in the fall. Walker is on the RGA’s executive committee.

“Wisconsin is moving forward, but there’s more work to be done. The Republican Governors Association is proud to support Governor Scott Walker’s re-election,” said RGA Chairman Chris Christie of New Jersey in a statement.

The off-year electorate in Wisconsin, a purple state, has tended to favor Republicans. Burke's challenge is to get liberal voters tempted to sit out the midterms to come out.

“Wisconsin can do better and will do better under Mary Burke,” said Democratic Governors Association Chairman Peter Shumlin of Vermont in a statement.

Walker occupies a unique spot in the early 2016 sweepstakes. He's beloved by conservative activists and large donors. And he's a Midwesterner in a prospective field of blue chip Republicans from the Northeast (Chris Christie) and the South (Rand Paul, Jeb Bush, Marco Rubio and Bobby Jindal).

But his appeal would instantly be erased by a loss to Burke. Donors and activists simply aren't inclined to back someone who is fresh off being tossed out of office.

At a Christian Science Monitor Breakfast last November, Walker told reporters he was keenly focused on the 2014 midterms -- not just because of his own election, but also because 2016 won't "matter as much" if a Republican president did not have a Republican Congress.

But if Walker doesn't win his reelection campaign, 2016 won't likely matter for him at all.