An increasing number of voices in the media and political class are crowning Mitt Romney as the inevitable Republican nominee.  As I wrote in my column earlier this week, while I believe 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 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 Republican presidential nomination, voters have shown great reluctance in anointing someone too quickly. They have put up various road bumps along the way. In 2000, when George W. Bush came back after losing the New Hampshire primary and won South Carolina, and everyone thought he was now on a path to victory, he lost the Michigan primary three days later.  In 2008, John McCain won New Hampshire, and then a week later lost Michigan to Romney.
3. Romney has not come under a concerted and sustained negative attack by any candidate yet. Other candidates have had to endure this, but Romney has avoided it. This will happen at some point very soon, and he and his campaign will be tested.
4. Up until Tuesday's Iowa caucuses, Romney has shown no capacity over the course of this campaign to grow his support above 30 percent outside of New Hampshire. This will become more and more of a problem as the field is winnowed 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 still remains very vulnerable on the authenticity question. This will remain an area an opposing candidate could still take advantage of.

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