Consultant: you're welcome. as a first step, our team analyzed the other potential primary contenders. the reality is that with such a strong field, it is going to be difficult to gain the of votes necessary to avoid a runoff—unless you want to go negative from the start. and our opposition research team found plenty of ammunition to do just that.
...it is going to be difficult to gain the Majority of votes necessary to avoid a runoff.
The consultant here seems to be referring to a Runoff type of election where there are two rounds to voting. In this type of election, when no contender gets over 50% of the votes which is considered a Majority, the election goes to a second round with the highest 2 contenders or in some cases the contenders past a certain threshold then contending amongst themselves.
The Consultant is telling the candidate that the other candidates are quite strong so them getting the Majority vote required to avoid a second round will be tough.