Slate says the Ron Paul train is running out of steam:

According to the campaign's February FEC statement — its last monthly update — it had $1,644,814.60 in the bank after spending $5,233,011.28 in the packed primary month of January. Four years ago, Paul had $6,017,400.79 left in the account at the end of January.

This, in itself, is not a sign of Paulian weakness. Ask any veteran of the 2008 Paul campaign, and they'll tell you that the late surge of moneybombs and media interest came too late to build a strong campaign where they needed one. That wasn't a problem this time. The money came in briskly throughout 2011. But it hasn't been gushing like it used to. A January "moneybomb" netted the campaign $1.3 million; a moneybomb at the same point in the 2008 race brought in $1.85 million.

Ron Paul's energy has been flagging since Iowa, and his campaign has been coasting on the energy of the very enthusiastic Ron Paul supporters who have already fallen for the candidate. The problem is, if your candidate isn't putting out the energy he used to, you're not going to draw new supporters to the campaign. This is basic thermodynamics, and it's plain for anyone to see: Ron Paul is over. His supporters are practically a nostalgia act from 2008 at this point.