I decided to change my comment into an answer.
Please be forgiving when I suggest that you need a thicker skin. The Church was much more politically active before 1980. Around that time, the IRS began cracking the whip about 501(c)3 non-profit organizations dabbling in politics and the Church changed its general policies to reflect that. In our modern "politically correct" world we take very quick offense when things aren't "just right," but Bishops (all 31,000 of them) are imperfect too.
As remarked in Ella's answer and your comments, Bishops live in two worlds: one is personal, the other is (ecumenically) "professional." Anyone (like myself) who's had to walk that tightrope knows it's impossible to walk it perfectly.
Joseph Smith once remarked that a prophet is only a prophet when he's acting as such. Bishops, like prophets, have personal lives and are allowed complete freedom within gospel law to live those lives. In other words — your bishop has the right to participate in politics as he sees fit and to use his Constitutional right to free speech. In other words, no bishop has the right to endorse any politician or political issue as a representative of The Church of Jesus Christ of Latter-day Saints, but every bishop has the right to hold his own opinions and to express them.
You've given us no details. You should have. What public forum? Over the pulpit? Talking to a dozen members in front of a store? Chatting with friends at a ward picnic? What did he say? Would you feel the same way if he expressed an opinion that you agreed with? Do you feel that he was using his calling as bishop to unduly influence others toward his opinion?
My worry, since we have no details, is that it's possible the problem is yours, not his. It's worth remembering that not speaking evil against leadership basically means to cut them some slack. I've witnessed prophets do things that raised my eyebrow... but they're human, just like the rest of us, and when I weighed their actions against all of scripture and the Grand Scheme of Things, I found that they were doing the best they could, just like me, and since no harm was done, it was me who had to be more forgiving and understanding.
So, instead of informing on him, try talking to him first.