There is lots of buzz that Marco Rubio is inching up in Iowa.

There also seems to be a loose consensus that Rubio had the better of the debate last night.

So Ted Cruz is turning his attention to Rubio with a negative ad campaign that previously was focused on Trump. The NY Times reports:

Senator Ted Cruz, scrambling to put down a growing threat in Iowa from Senator Marco Rubio, is shifting nearly all of his negative advertising from Donald J. Trump to Mr. Rubio for the final three days of the caucuses.

Mr. Cruz intends to direct his firepower at his Senate colleague after days of seeing Mr. Rubio inch up both in public polling and his own private surveys, according to two advisers to Mr. Cruz who spoke on the condition of anonymity. After leading in the polls in Iowa for much of the last month, Mr. Cruz has slipped into second behind Mr. Trump in most public surveys.

The change of direction marks an abrupt shift, reflecting how volatile the race in Iowa remains: Mr. Cruz’s campaign only began airing negative spots against Mr. Trump this week and just put their first attack ad up against Mr. Rubio on Thursday on Iowa television.

Cruz also is running positive ads, but the negative turn could be a sign of trouble.