Senate Minority Leader Mitch McConnell (R-Ky.) will have to fend off challengers from both sides to win re-election.

Matt Bevin, a Louisville businessman and Tea Party candidate, is set to announce this week that he will take on the five-term incumbent in a GOP primary next year. Bevin has already locked up air time and will make a formal announcement Wednesday, before setting off on a three-day blitz around the state to promote his candidacy.

Bevin's entrance into the race raises the stakes for McConnell, a deeply unpopular senator who already appeared to be headed toward a bruising, if ultimately favorable, general election campaign.

A PPP survey in December found that McConnell was the most unpopular senator in the nation; he earned a 37 percent approval rating, with a strong 55 percent majority of registered voters in Kentucky saying they disapproved of his job performance. Those numbers have both ticked down one percentage point since then, according to an April PPP poll, leaving him still highly vulnerable to a strong challenger.

That second poll had another piece of bad news for McConnell, since it showed the Democratic Senate candidate, Secretary of State Alison Lundergan Grimes, trailing by just a four-point margin.

That's assuming McConnell even makes it through a primary challenge.

That same PPP poll found that while 46 percent of GOP primary voters supported McConnell in a hypothetical primary, 32 percent said they would prefer someone more conservative. Another 22 percent were undecided. A Courier-Journal poll earlier in the year showed Republicans being similarly tepid, with just 34 percent saying they would support McConnell against any challenger, versus 53 percent who said they would first need to see who else ran.

While McConnell isn't as unpopular within his own party as other former GOP pols who went down in bitter primary challenges — two-thirds of Florida conservatives disliked former Gov. Charlie Crist when he ran for Senate — there is still significant room to his right for a primary challenger to at least make things interesting.

Sensing that space, McConnell has moved in the last year to shore up support with conservatives and Tea Party types. He even hired Sen. Rand Paul's (R-Ky.) former campaign manager, Jesse Benton, to run his operation.

In 2010, Paul successfully toppled former Kentucky Secretary of State Trey Grayson in a primary battle. With the backing of Washington Republicans, including McConnell, Grayson led in the early going, though Paul ultimately won the election by characterizing his opponent as a career politician.

Bevin could use that same attack on McConnell, who will be seeking a sixth Senate term in 2014. And given McConnell's grudging deal-making with President Obama and Democrats in the Senate, there would be plenty of fodder to cast McConnell as a more moderate legislator.

McConnell angered conservatives earlier this year for striking a budget deal that raised taxes, and he drew their ire for not killing or watering down the massive immigration bill before it went on to the House. Most recently, some on the right felt betrayed that McConnell agreed last week to move through Obama's cabinet nominees to avert a filibuster showdown.

A lot will depend on Bevin's campaign skills, which have bedeviled first-time Tea Party challengers in the past (see: Christine O'Donnell). Also, with McConnell boasting a $10 million war chest, Bevin will need cash and serious grassroots support. According to Alexander Burns at Politico:

In the run-up to his anticipated campaign, Bevin has spoken with leaders of at least three national right-leaning advocacy groups: the widely feared Club for Growth, the Jim DeMint-founded Senate Conservatives Fund and the Madison Project, a small-government group chaired by former Kansas Rep. Jim Ryun.

Those organizations aren’t yet commenting on Bevin, given that he hasn’t declared his campaign. [Politico]

The McConnell camp has already gone on the offensive against Bevin, calling his encroachment a "nuisance." Bevin could very well become much more than that down the road.