I can provide arguments in favour of the position but not definitive proof, you can decide whether all of this is just "circumstantial".
- First day of war, Trump praises Putin for his behaviour, on tape, call him a genius [1, 4].
- Second day of war, Trump doubles down, on tape. [1]
- When asked whether [Trump] made a mistake calling [Putin] a genius, Moskow Mitch dodges the question, responds that Putin is a "ruthless thug". [2]
- [Repeatedly] met with Putin with no staff / note takers. [3]
- [The first time] Trump was impeached over holding aid of $400m from Ukraine. [4]
- Trump sides with Russia against FBI at Helsinki summit [5]
- Trump veto'd sanctions against Russia [6]
- Trump says it's 'common sense' to include Russia in G7 [7]
- Trump revealed highly classified information to Russian foreign minister and ambassador [8]
- Trump offered to help Putin with wildfires while ignoring wildfires in US [9, 10]
And the list keeps growing, consider looking into Manafort under the light of these events.
As for Schroeder, consider that he pushed for gas, is a close friend of Putin and didn't extend lifetimes of Nuclear plants, and after leaving his position he became board member in Gazprom [11, 12, 13]
[1] https://www.independent.co.uk/news/world/americas/us-politic...
[2] https://www.newsweek.com/mitch-mcconnell-calls-putin-ruthles...
[3] https://www.vox.com/2019/1/29/18202515/trump-putin-russia-g2...
[4] https://www.businessinsider.com/trump-statement-ukraine-cris...
[5] https://www.bbc.com/news/world-europe-44852812
[6] https://www.nytimes.com/2017/07/27/us/politics/senate-russia...
[7] https://www.reuters.com/article/us-g7-summit-trump/trump-say...
[8] https://www.washingtonpost.com/world/national-security/trump...
[9] https://www.reuters.com/article/us-usa-russia-trump-putin-wi...
[10] https://democrats.org/news/fact-sheet-trump-ignored-and-refu...
[11] https://www.politico.eu/article/outrage-germany-ex-chancello...
[12] https://www.thisismoney.co.uk/money/markets/article-10562307...
[13] https://www.theglobeandmail.com/world/article-former-german-...