Chris Gabrieli’s decision to jump into the race for governor — which he’ll do this week, if all goes according to plan — has an almost Shakespearean quality. Consider: at the end of January, attorney general and would-be governor Tom Reilly was poised to pick Gabrieli as his running mate, but changed his mind at the last minute and tapped state representative Marie St. Fleur instead. The about-face stunned Gabrieli; worse, when St. Fleur’s financial woes led her to quit after one day, it exacerbated doubts about Reilly’s political skills. and now, two months later, Gabrieli is challenging his erstwhile ally for the state’s top job.

Betrayal! Irony! Revenge! All great stuff, if you like political theater. But Gabrieli, a venture capitalist best known as Democrat Shannon O’Brien’s 2002 gubernatorial running mate, can’t afford to be typecast as a grudge candidate. He’s already got the 500 signatures necessary to get into June’s Democratic state convention — more on that later — but he’ll need votes from around 300 extra delegates to land a spot on the primary ballot. And prospective supporters might balk if they decide that Gabrieli’s campaign is just about payback.

Which, to be fair, it isn’t. After all, Gabrieli has a long history of political and civic activism. He ran for Congress in 1998, and for lieutenant governor in 2002. He chaired MassINC, the influential nonpartisan think tank, for six years. And he co-founded the nonprofit Massachusetts 2020.

Consequently, when the Phoenix asked Gabrieli why he wants to be governor, his answer — he loves Massachusetts, and a groundswell of popular support convinced him to enter the race — was largely convincing. “Our state is stagnating; it’s losing its fastball,” Gabrieli said. “And I find that incredibly frustrating ... Our track record of getting results for people, both in the private sector and in the public sector, puts me in a position to step forward as governor and say, ‘Here’s some things we can really do. And I will get them done.’ ”

And yet. However noble Gabrieli’s intentions are, whatever popular pressure may have pushed him to enter the gubernatorial fray, there seems to be a glimmer of residual resentment. Take this line, which seems like an obvious swipe at Reilly’s Kerry-esque positions on gay marriage and the death penalty. “I think that it’s really important that candidates for office can answer, really briefly, where they stand on issues that people care about, and tell people what they think is right and wrong,” Gabrieli said. “I’m for gay marriage. I’m pro-choice. I’m against the death penalty.”

Three’s company
Whatever blend of altruism and ego is fueling Gabrieli’s candidacy, Massachusetts voters should benefit from his entry into the race, at least in the short term. With just Reilly and Deval Patrick vying for the Democratic nomination, the primary contest could have been a monotonous battle of caricatures: in one corner, the Boy from Springfield, a humble everyman who wants to show us his tax returns; in the other, the candidate known simply as Deval, whose social liberalism, Alger-esque life story, and existential take on politics make the faithful swoon.

With the arrival of Candidate #3, though, the picture changes. Gabrieli is a grade-A wonk who loves parsing social and economic minutiae; when he talks about an untried idea he’d like to put to the test, he exudes an almost childlike eagerness. It’s a good bet that, as the campaign progresses, Gabrieli will insist on discussing a number of esoteric subjects in great detail: the favorable consequences of expanded after-school programs; cutting health-care costs by reforming bureaucracy; indexing the income tax to economic growth. And as Gabrieli gets down and dirty in the public-policy muck, Reilly and Patrick will have to do the same.

Or will they? Unlike Patrick and Reilly, Gabrieli didn’t participate in the February caucuses of the Massachusetts Democratic Party (MDP). Still, by getting signatures from 500 delegates afterward, he earned the right to attend the Mass Dems’ June convention, where the party’s primary line-up will be finalized. (Thanks to a new rule, candidates need to win 15 percent of the delegates’ votes in the first round of voting to get their names on the ballot.)

The bad news, for Gabrieli and his supporters, is that some Democrats see his upcoming presence at the state party convention as a miscarriage of justice. MDP rules state that anyone taking Gabrieli’s path needs to garner support from 500 elected delegates. But when Gabrieli started weighing a run, the party’s general counsel ruled that these signatures could be obtained both from delegates elected at the caucuses and from “add-on” delegates — an appointed group that includes current and former office-holders, women, minorities, and persons with disabilities.