Gov. Charlie Baker wants to get to the bottom of how the Green Line Extension project developed upwards of $1 billion budget deficit.

Because of a combination of increased construction prices, other unforeseen costs and a failure to budget for either, the governor now has two big problems on his hands when it comes to the Green Line extension through Somerville to Medford.

"We have to figure out how we can get the thing down from something closer to $3 billion to something like what it was originally budgeted at," Baker said. "And secondly, we need to figure out if we have some process issues we need to fix. This can't happen again."

He can scale the project way back and look for new funding methods. Or — and he doesn't want to — he could just cancel the whole project, which is already underway.

And all this after the federal government seemed to save the project last year by agreeing to contribute $1 billion of their own.

Somerville Congressman Mike Capuano's been in the thick of the green line funding fight for twenty years:

"My thoughts were very simple," Capuano said. "It was like 'Oh, god. Here we go again. It never stops.'"