President-elect Barack Obama's 3 million campaign volunteers got re-enlistment notices this week. Campaign manager David Plouffe, in a mass e-mail sent Wednesday to former workers, asked how much time they can spare for four missions integral to Obama's effort to transform his victory into a broader political movement. The volunteers' options are, Plouffe wrote: -Campaign for progressive state and local candidates -Undertake grassroots local efforts to advance Obama's agenda -Train others in Obama's organizing techniques -Focus on local political issues. "Obama's building a political machine," said Stephen Hess, a presidential scholar at the Brookings Institution, a center-left Washington research group.