Leading up to the infamous Star Wars moment of Order 66, the Jedi made a lot of huge mistakes. Naturally, a big one was somehow not noticing the powerful Sith Lord who they met with on an almost daily basis. But another error was not making good use of all the resources at their disposal. That included former Chancellor Valorum, who could have provided some key insights that may have helped them.
Many fans could be forgiven for not remembering Finis Valorum. His only major appearances were in The Phantom Menace and in a single episode of The Clone Wars. But as the former Chancellor of the Galactic Republic, Valorum was arguably a key figure in the overall Star Wars universe. Or, at least, he should have been.
The first step in then Senator Palpatine's secret plan to take over the galaxy involved removing Valorum from power. He staged the Trade Federation blockade of Naboo to give Queen Padmé Amidala the leverage she needed to call for Valorum's removal. While Palpatine suffered some losses, such as the apparent death of Darth Maul, his ploy was an overall success and he became the new Chancellor.
After his departure from political life, Valorum largely retreated to his estate on Coruscant. He did not come up again until Season 6, Episode 10 of The Clone Wars. This was several years after he was removed from power, and the war was in full swing. The Jedi were finally getting around to investigating the origins of the Clone Army. As such, Yoda went to Valorum for information on a deceased Jedi Master named Sifo-Dyas.
This meeting appeared to be the first time that Yoda or anyone else from the Jedi Order had made contact with Valorum since he was removed as Chancellor. More than 10 years had elapsed between those events, and a lot had changed in the universe. As the former Chancellor of the Galactic Republic, Valorum was likely privy to a shocking amount of sensitive information. And he probably would have been happy to share it, had he been asked to.
Keeping in mind that Valorum could have provided the Jedi with a lot of intel, this is a further indictment over their acceptance of the situation. It was years into the war before they seemingly put any effort into exploring the origins of the Clones, beyond what Obi-Wan Kenobi learned in Attack of the Clones. This army that appeared out of nowhere at the perfect moment was one gift horse that they should have looked in the mouth.
The Jedi's mistrust of Palpatine had started early in war, yet they didn't do the obvious thing and speak with former Chancellor Finis Valorum. It was yet another mistake in a long line of mistakes they made while focusing too much on the war effort itself. And ultimately, that's exactly what Palpatine wanted. His plan only succeeded because the Jedi played so willingly into his hands.