“The issue of collusion is still open,” Mr. Burr said.

The news conference was the most extensive since the committee began its investigation of Russian meddling in the 2016 election early this year and the first time the senators have detailed so fully the trajectory of their secretive investigation and their sense of the stakes. Both men come from swing states where the presidential campaign was fought aggressively.

That appeared to have made an impression.

“There needs to be a more aggressive whole-of-government approach in terms of protecting our electoral system,” Mr. Warner said. “Remember, to make a change even in a national election doesn’t require penetration into 50 states.”

He added, “You could pick two or three states in two or three jurisdictions and alter an election.”

The Senate Intelligence Committee is one of three committees on Capitol Hill that have opened full-fledged investigations into the relationship between Mr. Trump, his associates and Russia. Given the committee’s jurisdiction over the intelligence community and a strong working relationship between Mr. Burr and Mr. Warner, it has been considered the congressional committee most likely to deliver a substantive report on Russia’s covert efforts.

Mr. Burr and Mr. Warner sought to inspire confidence on Wednesday that the committee remained on course to do so. They later got a boost from Representative Adam B. Schiff of California, the ranking Democrat on the House Intelligence Committee, who said he concurred with their statements based on his committee’s work.

The senators said that their investigators have pored over nearly 100,000 pages of classified intelligence and documents turned over by the Trump campaign and other associates of the president’s, and they have conducted more than 100 interviews with many of the top officials connected to both the Trump campaign and the intelligence community. Investigators also recently received material from Facebook and, to a lesser extent, Twitter, about advertisements on their platforms linked to Russia.