I have not listened to his DNC speach, but back in january he introduced a resolution that would have invoked the legal requirement that US assistance not be used to commit human rights violations. It failed 72-11.
Back in April, he spoke in the senate opposing the $8.9 billion offensive military aid to Israel; after having introduced amendments to cut those provisions out. (If you read 1 link from this post make it this one).
As early as October 11, he was calling for the US to force Israeli restraint, and explicitly calling Israel's responce a violation of international law
On October 25, he demanded information on how Israel was going to use the first aid package before it went to a vote in the senate, which was formally sent to Biden November 1.
At this point I stopped going through his press releases, because at this point, he just sounds like a Cassandra.
The problem with Israel is that its leader was a bit too vile. About half of the elected knesset refused to form a coalition government with Netenyahu, resulting in years of failing to form a governing coalition.
Eventually, the path out of the stalemate ended up being forming a coalition with far right members of the knesset that had previously been political pariahs; including appointing a convicted terrorist to the role of minister of national security.
Prior to October 7, this was an extremely tenous political position. The coalition was hanging on by a thread. The attempted judicial ~~coup~~ reform was stopped by massive public backlash. And the politian whose divisiveness was central to the political crises that enabled the far right to join the coalition was in the middle of defending himself in a criminal trial. However, when a crisis like October 7 happens, you are stuck with the leaders you have. And Israeli leadership at the time was possibly the worst in the history of the country for handling it (unless you agree with their manifest destiny version of Zionism, in which case I think they are doing quite well).