In this use, I think that 'pitch' could be interpreted two ways, and it is possibly deliberately meant to have a double meaning, or be ambiguous. A 'pitch' is the set of techniques that you use to persuade someone of something. The most common use is a 'sales pitch', when a salesperson tries to persuade someone to buy their product. A sales campaign, or an electoral campaign is similar to, or at least would contain a pitch of some sorts. 'Pitch' can also be related to musical pitch - high pitched, or low pitched. It is also often used more figuratively, and in this case, it could mean that he 'sped up' his campaign, making it higher pitched, i.e faster and more aggressive.