Story highlights Cruz's super PACs, Keep the Promise, have raised only around $2 million in the second half of 2015

The figure is a significant slowdown and shows the group has not expanded much beyond the original anchor donors

(CNN) The main super PACs supporting Texas Sen. Ted Cruz's presidential campaign only raised a few million dollars in the second half of 2015, a modest sum that far trails the huge checks they collected in the opening days of the campaign.

Cruz's super PACs, Keep the Promise, have raised only around $2 million in the second half of 2015, according to two people familiar with the figures. The groups have raised up to $5 million in the month of January, the sources said.

That's a far cry from the $38 million raised in the first half of 2015, most of which came in the opening days of Cruz's bid.

That sum for Keep the Promise is a significant slowdown and shows the group has not expanded much beyond the original anchor donors that made the group into a surprise story of early 2015. Three families are responsible for $36 million of the roughly $40 million the super PACs raised in 2015, and it does not appear additional donors of the same scale have been landed during the second half of 2015.

Because Keep the Promise is funded by three large family investments, group officials say additional fundraising was not a strategic priority. It only hired a professional fundraiser this fall, and Keep the Promise has hosted just a few fundraising events.

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