A big-money campaign is using misleading Obama ads to prop up an establishment Democrat, bad news for the left-wing challenger and for honest campaigning.

• In Michigan's Democratic Senate primary, establishment pick Haley Stevens is running ads that make voters think Obama endorsed her — he hasn't.
• The ads recycle old Obama praise from the 2010 auto bailout, and some voters are switching to Stevens because they wrongly believe Obama backs her.
• Tens of millions of dollars, some tied to AIPAC and corporate groups, are flooding in against left-wing challenger Abdul El-Sayed, who is now tied in the polls.
• The tactics are getting dirty: the auto workers union endorsed El-Sayed but had to send a cease-and-desist after a pro-Stevens group used its logo.
• The sitting senator, who promised to stay neutral, jumped in for Stevens once El-Sayed closed the gap.

Outlook: The race is close, and whether these Obama-branded ads swing older primary voters will decide it.