So far this week, Barack Obama has been endorsed by 13 previously uncommitted superdelegates and picked up two switchers who had previously endorsed Hillary Rodham Clinton. Clinton picked up two new commitments, but that only offsets the two defectors. Her lead among superdelegates, which was just under 100 in early February, is down to a new low of 6.5 (yes, there are superdelegates who get half a vote). These numbers are according to the count maintained by the excellent demconwatch. There are other counts, but they are close to one another.

The story in this morning's Strib by my esteemed former colleague Bob Von Sternberg quotes Clinton supporters who resent the way she is being pushed out of the contest. The sentiment is understandable, but doesn't bear much scrutiny. No one can force Clinton to leave the race. All they can do is endorse Obama, complain about how the continuation of the contest is hurting the party, and perhaps develop a grudge over it. And that's been going on for a couple of months without forcing Clinton out.

Clinton is surely calculating, on an almost daily basis, whether the shrinking chance that she can become the nominee is worth the growing damage to her standing in the Democratic Party, and how that damage might affect her future political ambitions, whether to be Obama's running mate, to make a future presidential bid, or to rise within the party leadership in the Senate.

Obama's overall delegate lead is up to a new high of 157.5 (1853.5 to 1696). (This morning I had misstated that as 275.5. My thanks to reader D.H., who alerted me to the error.)

From here, Clinton would have to win two-thirds of the remaining uncommitted delegates (super and mortal combined, counting the 19 who are committed to John Edwards). This is not unthinkable, but highly unlikely and growing more so with every new superdelegate commitment she loses.

And one last note. We should pay little attention to the statements that some reporter wrings out of Clinton almost daily to the effect that she's staying in the race until it's over. Like Edwards — who campaigned hard and swore he was staying in until the convention until moments before he dropped out — it is not reasonable to expect Clinton to candidly discuss how close she is to dropping out. She'll tell us when she does.

Afternoon update:
The above was written this morning. Obama has rolled out two more superdel endorsements, giving him a net (counting the switchers) of 17-1 for the week. By DemConWatch's count, that reduces the Clinton superdel lead to 4.5. (Based on those latest endorsements, ABC, which has a different scorecard, is now the first of the many media organizations that are tracking superdelegates to claim that Obama has pulled ahead in superdelegates).