There was definitely meaningful involvement by the Trump campaign in Russia's efforts to undermine the 2016 election.
One example...
5. June 9, 2016 Meeting at Trump Tower
On June 9, 2016, senior representatives of the Trump Campaign met in Trump Tower with a Russian attorney expecting to receive derogatory information about Hillary Clinton from the Russian government. The meeting was proposed to Donald Trump Jr. in an email from Robert Goldstone, at the request of his then-client Emin Agalarov, the son of Russian real-estate developer Aras Agalarov. Goldstone relayed to Trump Jr. that the “Crown prosecutor of Russia . . . offered to provide the Trump Campaign with some official documents and information that would incriminate Hillary and her dealings with Russia” as “part of Russia and its government’s support for Mr. Trump.” Trump Jr. immediately responded that “if it’s what you say I love it,” and arranged the meeting through a series of emails and telephone calls.
At the same time, that wasn't enough evidence to charge most members of the Trump campaign under existing laws.
C. Russian Government Outreach and Contacts
As explained in Section IV above, the Office’s investigation uncovered evidence of numerous links (i.e., contacts) between Trump Campaign officials and individuals having or claiming to have ties to the Russian government. The Office evaluated the contacts under several sets of federal laws, including conspiracy laws and statutes governing foreign agents who operate in the United States. After considering the available evidence, the Office did not pursue charges under these statutes against any of the individuals discussed in Section IV above—with the exception of FARA charges against Paul Manafort and Richard Gates based on their activities on behalf of Ukraine.