Republican presidential candidate, Sen. Ted Cruz, R-Texas, listens to a question during a campaign event Jan. 7, 2016, in Webster City, Iowa. (AP Photo/Jae C. Hong)

The best-known Super PACs supporting Texas Sen. Ted Cruz's presidential bid raised only slightly over $1 million dollars in the second half of 2015, a small amount compared to the totals reported by Cruz's network of "Keep the Promise" Super PACs in the past.

Cruz stunned the Republican field during the first half of 2015, raising $38 million for four connected Super PACs using the name "Keep the Promise."  Most of that money was raised during the early days of the Texas senator's  presidential bid and the money came from a handful of large donors, including $11 million from Robert Mercer, the co-CEO of a New York hedge fund and an additional $15 million from Farris and Dan Wilks, billionaire brothers  from Cisco, Tex., who made a fortune in the fracking business.  Because of the Super PACs early fundraising success, Cruz allies said that additional fundraising from large donors was not a top goal in the final quarter of the year.

Instead the Super PACS supporting Cruz concentrated on spending  to support the Texas senator in the weeks before the Iowa caucuses, which start Monday. Cruz Super PACs have run ads in the past week attacking his leading  GOP competitors.  One used a 1999 interview in which Donald Trump told the late Tim Russert that he is "very prochoice in every respect."

All told, Cruz's presidential bid has received support from  more than half a dozen super PACs, which reported spending nearly $10.6 million on his behalf in the last quarter. Super PACs started in 2010 after a Supreme Court decision sanctioned unlimited donations to independent political committees by individuals, corporations and unions. The newest of these groups backing Cruz, Stand for Truth, raised nearly $2.5 million between its formation in mid-November and the end of December. The organization has said it would spend $4 million on advertising to benefit Cruz in Iowa and South Carolina. One "Stand for Truth" ad running in Iowa recently was critical of Sen. Marco Rubio (R-Fla.) for supporting a failed Senate bill that would have granted a pathway to citizenship for undocumented immigrants.