Iowa Republicans voted Saturday to keep the Ames Straw Poll for one main reason: It's a cash cow.

Despite continuing questions about its usefulness and a campaign by Iowa Gov. Terry Branstad (R), among others, to bring it to an end, it will be back this year as the earliest informal vote of the 2016 Republican presidential primaries.

And indeed, as long as it's bringing in the kind of attention and money it did in 2011 -- a reported $1.5 million before expenses, and about half of that afterward -- the state party is likely to continue to find a place for it.

About the only thing, it seems, that will end the straw poll is when it no longer brings in the dollars. But we might be on our way.

The last two straw polls have seen no real participation from the eventual GOP nominee and an increasing number of votes going to candidates with very little chance of winning much of anything -- much less the Iowa caucuses or the GOP nomination.

The chart below shows how much of the Ames Straw Poll vote was carried by both the winner of the eventual Iowa caucuses and the winner of the Republican nomination.

Clearly, the straw poll has become less and less of a priority for formidable candidates and less and less predictive of both the Iowa winner and the national winner.

But that's not really news. Here's another way to look at this: The chart below shows how many of the votes have gone to a candidate who went on to win a state in the nominating process, vs. how many went to candidates who never won a state.

In 2011, nearly 85 percent of the votes were won by Ron Paul, Michele Bachmann, Tim Pawlenty, Herman Cain, Rick Perry, Jon Hunstman, Thaddeus McCotter and others who never won a state.

In large part, this is because Mitt Romney didn't participate and Newt Gingrich's campaign didn't actively seek votes. The same could be said of 2007, when John McCain didn't participate.

But the fact that these front-running candidates think that they can skip the expensive event and still do just fine in the race is both symptomatic of the straw poll's problems and the reason it might struggle to last far beyond 2015.

The more times the straw poll looks like it did 2011, the less you'll see candidates bother to show up. In 2015, it's not hard to see possible candidates such as Jeb Bush and Romney and Chris Christie skipping it. The process just isn't worth the investment for them.

And the more folks like that skip the straw poll, the less predictive it will become of the race ahead, and the less emphasis and money will flow to the event. If candidates like Bachmann and Paul and Cain dominate the straw poll again in 2015, the straw poll loses even more oomph for 2019.

The 2011 straw poll wasn't bad enough to kill the straw poll. We'll see this year -- and beyond -- whether it retains anything amounting to its former status.