WASHINGTON (Reuters) - Wary Democrats on Thursday challenged Republicans who control the U.S. Congress to conduct a credible investigation into contacts between President Donald Trump’s associates and Russia, a process that will likely take months and may never become public. “We will be watching very carefully. If the Intelligence Committee investigation is not proceeding to unearth the entire truth, we will seek alternative tools and structures to get to the truth, because get to the trust we must,” said Charles Schumer, the Democratic leader in the Senate. A growing number of Republicans showed their willingness to buck the White House and accept expanded congressional inquiries after the resignation of Trump’s national security adviser Michael Flynn over disclosures that he discussed U.S. sanctions with the Russian ambassador before taking office. Trump has reacted angrily in the aftermath of Flynn’s resignation, blaming journalists and blasting leaks. On Thursday, he dismissed a growing controversy about ties between his aides and Russia as a “scam” and a “ruse,” perpetrated by a hostile news media. But without the authority to hire a Watergate-style special prosecutor or convene a special committee, Democrats will have to rely on the Republican-led Senate and House of Representatives’ Intelligence Committees to demand classified documents and get to the bottom of any ties between Trump’s associates and Moscow. After eight years with a Democrat in the White House, Republicans want to work with Trump and his administration to advance their party’s legislative priorities, from repealing Obamacare to rolling back regulations and cutting taxes. But some congressional Republicans said they would support independent investigations only if committee-level probes proved inadequate. “The jurisdiction for counterintelligence programs falls on the Intelligence Committee, which is undertaking a bipartisan investigation, which I have full confidence will ... do a very good job and conduct a serious inquiry,” said Senator Marco Rubio, a Republican member of the intelligence panel. “If it doesn’t, which would surprise me, then I’ll be one of the first ones out there to say that it didn’t do so,” Rubio told reporters. A probe could take a year or more, in part because U.S. intelligence agencies have just begun to gather and analyze material. There will likely also be deep partisan divisions over which of its findings could ultimately be released. Democrats and Republicans have not agreed on the scope of an investigation. Democrats want Flynn to testify in a public hearing, but Richard Burr, the Senate Intelligence Committee chairman, has said only that public hearings would take place when they are appropriate. Some Democrats had questioned Burr’s commitment to a thorough investigation, but Schumer said on Thursday that Burr “is now working well” with Senator Mark Warner, the top Democrat on the Intelligence Committee. Senator Ron Wyden, another Democrat on the intelligence panel, said there would be “tough battles” ahead. Partisan divides are deeper in the House, where many Republicans - like Trump - have focused on the dangers posed by leaks from his White House, rather than aides’ potential ties to Russia. Rep. Devin Nunes, the Republican chairman of the House Intelligence Committee, questioned whether the recordings of Flynn’s conversations were even legal under federal surveillance rules. But critics say Republican calls for leak investigations may just be aimed at deflecting attention from possible misconduct by Trump aides. Paul Ryan, the Republican House Speaker, took a different view, telling his weekly news conference on Thursday: “If it’s classified information, that is criminal and there should be a criminal investigation of these leaks. That does compromise our national security.” 