Marco Rubio's decision to attend the Republican convention and speak for Donald Trump has exposed something important. Not about Rubio -- but about a lot of Republicans.
Yes, Rubio is clearly showing himself to be, as the Washington Examiner's Philip Klein says in a takedown, "an opportunistic politician with his finger to the wind."
After all, before he ran for the Republican presidential nomination, he had already gone from being an inside player in the Florida legislature to a tea party "outsider" when he ran for the U.S. Senate. He supported comprehensive immigration reform when it seemed to be where his party was heading, then repudiated it when anti-immigration sentiment regained the upper hand.
So what's wrong with that?
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Franklin Delano Roosevelt, the greatest president of the last 100 years, was an ambitious opportunist. The best two Republican presidents of the last 100 years, Dwight Eisenhower and Ronald Reagan, were ambitious opportunists.
Reagan's opportunism in particular should be a model for conservatives to emulate, since he was both a conservative ideologue and a politician "with his finger in the wind." Reagan, in both California and in the White House, proved ready to compromise when he couldn't get his way unilaterally, whether it was with the California Legislature, U.S. House Speaker Tip O'Neill or the Soviet Union. Nor was Reagan above abandoning unpopular positions to remain popular.
This is not to say that Rubio's decision to openly support Trump is the correct one for him. It may turn out that having supported Trump will be a black mark against Republican politicians if he loses against Hillary Clinton or is elected and performs terribly in office. If so, Rubio's sin will be poor judgment, not opportunism.
I'm not sure why Republican party actors took so long to settle on a candidate in 2015-2016, and then why support for Rubio was relatively weak once he emerged as their choice. Perhaps some Republicans were looking for someone with less obvious traditional ambition than Rubio or several other well-qualified candidates in the GOP race, such as Scott Walker or Bobby Jindal. Someone who (as Klein put it) would be an "idealist" or "an inspirational moral leader."
If so, it's no wonder they lost.
Bernstein is a Bloomberg View columnist covering U.S. politics.