Hillary Clinton picked up another high- profile endorsement Tuesday, this time from liberal Ohio Sen. Sherrod Brown. She can add him to the October list, which includes Sens. Thomas Carper of Delaware and Ed Markey of Massachusetts, and Govs. John Hickenlooper of Colorado and Jack Markell of Delaware.
Clinton has proved to be strong with liberals, as Vox's Dylan Matthews explains, yet has also pulled in backers across ideological, geographical and ethnic lines.
Endorsements might affect voters in a direct and an indirect way, as Seth Masket of The Washington Post's Wonkblog explained. First, voters can consciously seek the views of opinion leaders. Second, the visible endorsements (such as from governors and senators) indicate broader party support, and that, in turn, provides important resources to favored candidates. As Masket notes, there's evidence that both of these theories are correct, depending on circumstances.
Sometimes the effects may be relatively easy to measure. Which candidates attract the most volunteers and become the biggest fundraisers, for example? We can also ask voters if they are aware of endorsements and if they are affected by them.
Sometimes, however, it's all about the process.
Think, for example, about how Clinton survived her months- long slump. Relatively few big-name Democrats turned on her over the e-mail story. Bernie Sanders surged, but few Democrats said he was likely to win. When Joe Biden encouraged speculation in August and September about a possible announcement, hardly any Democrats outside of Biden's circle encouraged him. Clinton's repositioning on the Keystone pipeline and U.S. trade policy was mostly accepted.
It isn't just about high-profile Democrats coming to her support on TV (or at least not piling on). Reporters talking formally and informally to others in the Democratic party network were presumably hearing similarly positive things more often than not.
And Democrats were eager to tout Clinton's performances in the first Democratic debate and before the House Select Committee on Benghazi. Perhaps in the case of the debate the backers of Sanders didn't think she scored a triumph, but Democrats who were already committed to Clinton saw what they wanted to see.
Compare her continued strength with the demise of Scott Walker's candidacy or Jeb Bush's current slump. Without supporters of independent standing to vouch for a candidate, it's easier for the press to pile on when he or she stumbles - and all of them trip up at some point or another. Because of her solid party support, Clinton was able to continue generating resources even when she received bad press. Walker wasn't able to do this, and now Bush may be having the same problems.
Endorsements can't prevent a polling surge by another candidate - as Sanders has proved this year. Nor do they prevent slumps, which involve bad press and worried supporters. But having a large section of a party on a candidate's side makes things a lot easier -- even if this support can't always be quantified.
-- Jonathan Bernstein is a Bloomberg View columnist covering U.S. politics.
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