From the article:
If Cotton ran he would have little trouble raising money, although it might strike some as presumptuous for a freshman congressman to turn around and immediately run for the Senate — such sentiments probably hurt ex-Rep. Rick Berg (R-ND) in his ill-fated Senate run last year.”
As opposed to a junior Senator turning around and immediately running for President, because that's totally different, or something. I hope Mr. Cotton does a good job in the House, and it sounds like he will.