Lew has been serving, most recently, as White House chief of staff, a testament to Obama's confidence in his management skills.
For all the experience he brings and all the praise that's coming his way, Lew is also relatively untested in some important areas. His readiness to respond to a financial crisis, were it to occur on his watch, is unclear. And the next four years could be marked by important demands for financial leadership on the global stage, not just by maneuvering over domestic policy.
His potential nomination has been hovering in news headlines for weeks, as Mr. Geithner's expected departure neared. During that time, his name has sparked little controversy, in contrast to concerns that have arisen surrounding Chuck Hagel, Obama's nominee for secretary of Defense. The military veteran and former US senator has been under fire for everything from positions on Israel and Iran to an alleged antigay streak.
Still, some Senate Republicans may put up forceful opposition to Lew's nomination.