So it’s official: Elizabeth Warren is in. She’ll announce tomorrow that she will challenge Scott Brown for Senate. Here’s her statement:

“The pressures on middle class families are worse than ever, but it is the big corporations that get their way in Washington. I want to change that. I will work my heart out to earn the trust of the people of Massachusetts.”

I’ve already spelled out all the reasons national Dems want Warren to run right here. She can bring in tons of cash from liberals around the country (the Progressive Change Campaign Committee has already hauled in over $130,000 for her campaign), perhaps enabling her to go toe to toe with Brown’s financial juggernaut. As the driving force behind the creation of the Consumer Financial Protection Bureau, the centerpiece of Obama’s Wall Street reform bill, she’s extremely well equipped to draw a sharp contrast with Brown on issues relating to the economy and Wall Street.

National Dems also note that Warren’s bureau was a high profile target of the right for months, giving her experience in rebutting conservative attack lines in Congressional hearings and the media. Dems think she has already proven herself capable of fending off the most aggressive and determined of conservative assaults.

Republicans note that Warren still faces a crowded primary. As a professor from Oklahoma, they’ll argue, she’s exactly the wrong candidate to try to win back the sort of blue collar Dems from places like south Boston that powered Brown’s surprise win. Indeed, in a sign that Republicans will play the “liberal elitist” card heavily, they’re already referring to her as “Professor Elizabeth Warren.” Dems will counter that the circumstances of this run are vastly different: Last time, Brown had no record and faced a lackluster foe in a low-turnout special election. Warren is nothing if not energetic, and in 2012 statewide turnout could be far higher, with Obama at the top of the ticket and Brown getting linked to a GOP presidential standard bearer that’s to the right of the Massachusetts electorate.

One thing is certain: Warren’s entry into the race will have national implications, because she will be a rallying point for progressives around the country who are currently unhappy with the national Democratic Party’s drift from genuine, no-holds-barred, running-against-Wall-Street populism. The contrast between her approach and that of other national Dems will be interesting to watch. As someone who has waged a higher-profile campaign than perhaps any Dem against the financial institutions and titans that helped land us in our current economic crisis, Warren’s run could test the electoral limits of true populism in a way other Dems haven’t been willing to venture.