Here we go again in Massachusetts.

A little more than three years after Scott Brown's stunning special election upset win, Republicans are pinning hopes of a repeat on Gabriel Gomez, a first-time candidate who easily won the Republican Senate nomination on Tuesday.

There's a reason why Brown's win was so remarkable. That stuff simply doesn't happen very often. And the early read in the Bay State this time around is that it's unlikely to happen again.

Massachusetts GOP Senate nominee Gabriel Gomez. (Steven Senne/AP).

To understand Brown's win in 2010 is to understand the perfect storm that sunk Democrats' hopes that year. For starters, Brown was up against a flawed candidate, Attorney General Martha Coakley (D). Coakley dissed stumping in front of Fenway Park, seemed unfamiliar with Curt Schilling, and otherwise ran a poor campaign.

Brown, by contrast, was the ultimate feel-good story. He barnstormed the state in his pickup truck, which became a powerful symbol for his regular guy persona. If Coakley didn't already seem out of touch enough, Brown's easy demeanor and underdog attitude added insult to injury.

Then, there was the broader political climate. Backlash against President Obama's health care reform plan had enraged conservatives and a depressed economic climate didn't help him or his party. Later that year, Republicans would make historic gains at the ballot box as they seized back control of the House.

Fast forward to 2013. Having learned a painful lesson with Coakley, Democratic leaders resolved early to hand select a candidate for the seat once held by Secretary of State John Kerry. That candidate was Markey, the liberal dean of the congressional delegation. Senate Democrats, Kerry, and host of other influentials launched Markey with their full weight behind him. And he never looked back, cruising to victory in the Democratic primary.

Markey's not the flashiest candidate around. And he has some potential vulnerabilities, including the amount of time he spends away from the state. But Democrats will have an extra close eye on him, and anything that smacks of a misstep. He'll also have a lot of money in his war chest.

Gomez has an intriguing background. He's a former Navy SEAL and the son of Colombian immigrants. He can play the outsider card, and has cut a pretty moderate profile. In a letter he sent Gov. Deval Patrick (D) seeking an appointment to the Senate, he noted his support for Obama in 2008.

Still, this is deep blue Massachusetts. And already, Democrats have moved hard against Gomez, signaling a desire to define him before he defines himself. Statements from Democratic groups and the Markey campaign Tuesday night slammed Gomez's personal opposition to abortion, and hit him on guns and entitlements.

Here's what Gomez needs to do to win. First and foremost, he has to run the perfect campaign. In addition, Markey would have to run an awful one. And Gomez would have to raise tons of money and convince Republican groups to enter the race to support him -- something they may be hesitant to do, considering that a win would only buy time until 2014, when Gomez would be up for reelection again.

Defining Markey also will be a crucial component. The National Republican Senatorial Committee released a memo Wednesday telegraphing their intent to cast Markey as a creature of Washington and focus on independent voters. Really driving home that narrative will require expending substantial resources.

Coakley fed the narrative that she was out of touch with misstep after misstep. She was essentially doing the Brown campaign's job for him. If Markey doesn't end up being a train wreck -- and so far there are no indications he will be -- the burden will be on Gomez and his allies to define him. And that will be no small task.

Impossible? No. Unlikely? Very. That's the way the possibility of a Massachusetts upset on June 25 should be viewed right now.