Since I don't have a lot of time to dedicate right now (sadly!) I will try to list several things
1- First of all, his war regarding Vietnam was just part of bigger doctrine since Truman to contain communism. Civilians died, but no side was rather bright in the conflict. As person from post-communist state, I wish thete where persons in power in 1945 to stop bolshevik enslavement of Europe.
2- It was him who ended the draft for military.
3-It wasnt the senate but him who made EPA and new standards for ecology.
4-Nixon shock managed to knock around $17 billion off the deficit in three years.
Others have addressed how horrible the idea that "civilians die, so get over it" is. I'm going to address the fact that Nixon committed several war crimes in Indochina. To start with the bombing of Cambodia was indiscriminate, with many targets being rural villages that were thought to contain Communist troops. This violates Article 25 of the Hague Convention of 1907, which states "The attack or bombardment, by whatever means, of towns, villages, dwellings, or buildings which are undefended is prohibited." Hospitals were also routinely targeted, which violates Article 18 of the Fourth Geneva Convention ("Civilian hospitals organized to give care to the wounded and sick, the infirm and maternity cases, may in no circumstances be the object of attack, but shall at all times be respected and protected by the Parties to the conflict."). Operation Menu at least was also a violation of Cambodia's sovereignty, since the government of Prince Sihanouk didn't approve of the bombings. A lot of the stuff said here also applies to the bombings of North Vietnam.
And it's not like the bombing of Cambodia was the only time Nixon committed war crimes during the Indochina War. In 1965 the Johnson Administration started the Phoenix Program, which aimed to eliminate VC fighters, and the Nixon Administration continued this program until 1972. This program was also indiscriminate in its targeting, with civilians often murdered. To quote one US operative, standard procedure was to knock on the door of a suspect's house and "Whoever answered the door would get wasted. As far as they were concerned whoever answered was a Communist, including family members." This violates the Fourth Geneva Convention, which defines civilians as a protected class against whom violent acts cannot be committed. Torture of prisoners was also extensively used during the Phoenix Program. Prisoners are also defined as a protected class, and according to Article 32 of the Fourth Geneva Convention "The High Contracting Parties specifically agree that each of them is prohibited from taking any measure of such a character as to cause the physical suffering or extermination of protected persons in their hands" and goes on to name torture as one prohibited practice.
Nixon also attempted to cover up what happened at My Lai, and later tried to sabotage the trials of those responsible. This violates several sections of the Geneva Conventions, including Article 49 of the First Geneva Convention, which reads "Each High Contracting Party shall be under the obligation to search for persons alleged to have committed, or to have ordered to be committed, such grave breaches, and shall bring such persons, regardless of their nationality, before its own courts." My Lai was not the only time Nixon did this, and cover-ups of US war crimes was a systemic effort over his and several other administrations.
I could go on, but I think I've made my point. Richard Nixon was not only a war criminal, but a war criminal of a severe magnitude.