From the prolife lobbying group, Susan B. Anthony List:

I think you’ll also be interested in reading this letter Marjorie [Dannenfelser, president of SBA List] sent to all Republican presidential campaigns. As you may have seen in the news, some campaigns and their supporters have been attacking Sens. Ted Cruz and Marco Rubio for supposedly being “too pro-life” to win. Marjorie has called for an immediate end to these outrageous attacks – which are essentially the talking points of Planned Parenthood! 

As Marjorie explains in the letter, “an attack on [these] candidates’ pro-life positions is an attack on the pro-life movement as a whole.” (I encourage you to read the letter linked above. You can also read stories about the matter from Politico, CNN, and The Weekly Standard).