How effective are newspaper endorsements in influencing voter behavior?

The Des Moines Register announced its Iowa Caucus endorsements earlier this evening.

This year they endorsed Hillary Clinton ("a thoughtful, hardworking public servant who has earned the respect of leaders at home and abroad") and Marco Rubio (who "has the potential to chart a new direction for the party, and perhaps the nation, with his message of restoring the American dream.")  Here's the CNN report (2:11) announcing the paper's endorsements:

The Register began making editorial endorsements for the 1988 caucuses.  While possibly interesting at the moment, the Register has a mixed record of influencing the overall selection of the presidential nominees.  Here's a list they published that shows who they endorsed, who won the caucus, and who was the nominee:

1988

Republican endorsement went to Bob Dole and Dole went on to win the caucus.  But the nominee that year was George H.W. Bush.

Democratic endorsement went to Paul Simon but Richard Gephardt won the caucus.  Michael Dukakis was the Democratic nominee for president.

1992

No endorsements.

1996

Republican endorsement went to Bob Dole, who went on to win the caucus and Republican nomination.

2000

Republican  endorsement went to George W. Bush, who went on to win the caucus and Republican nomination.

Democratic endorsement went to Bill Bradley, but Al Gore went on to win the caucus and Democratic nomination.

2004

Democratic endorsement went to John Edwards, but John Kerry went on to win the caucus and Democratic nomination.

2008

Republican endorsement went to John McCain, but Mike Huckabee won the caucus.  McCain ultimately recovered and went on to the Republican nomination.

Democratic endorsement went to Hillary Clinton, but Barack Obama went on to win the caucus and Democratic nomination.

2012

 Republican endorsement went to Mitt Romney but that didn't help him win the caucus, which was won that year by Rick Santorum.  Romney came back, though, to win the Republican nomination.

What impact will today's endorsements have on the 2016 caucuses?  Politico is already speculating that the paper's endorsements could "backfire."

Classroom Connection: Ask your students: How effective are endorsements on influencing voting behavior?  To research that question, have them choose a newspaper and trace how effective an endorsement from that paper is on determining an election's outcome.