An increasing number of voices in the media and political classes are crowning Mitt Romney as the inevitable Republican nominee. As I wrote in my column earlier this week, although I believe that he has best odds today of winning the whole thing and is likely to do so, he is not inevitable.

Here are five reasons why we should be very cautious in getting too far out front of the voters:

1. So far in the six months of this campaign, we have had six different front-runners (some brief and some lasting a little longer). This nomination process has been the most topsy-turvy in modern times, and I expect we will have some more twists and turns ahead.

2. In the last few open races for the GOP presidential nomination, voters have shown great reluctance to anoint someone too quickly and have put up various road bumps along the way. In 2000, George W. Bush came back after losing the New Hampshire primary and won in South Carolina; everyone thought he was on the path to victory, but he lost the Michigan primary three days later. In 2008, John McCain won New Hampshire and then a week later lost in Michigan to Romney.

3. Romney has not come under a concerted and sustained negative attack by any candidate yet. Other contenders have had to endure such onslaughts, but Romney has avoided being targeted. This will happen at some point very soon, and it will test him and his campaign.

4. Up until Tuesday’s Iowa caucuses, Romney has shown no capacity over the course of this campaign to increase his support above 30 percent outside of New Hampshire. That will become more and more of a problem as voters winnow the field to only a few candidates. Romney must show at some point after New Hampshire that he can win a much larger share of the vote in places like South Carolina or Florida and beyond -- a big challenge for him.

5. Republican voters have shown a great desire for a candidate who is competent/electable/can be seen as a credible commander in chief, as well as authentic in their beliefs and a true conservative. Romney has the first half of this covered, but he remains very vulnerable on the authenticity question. An opposing candidate could still take advantage of this vulnerability.

Again, Romney is definitely the candidate to beat in this race, but let’s let this process play out for a while. So far, we have seen more twists and turns in this race than in a California yoga class.

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