Washington (CNN) In a political climate where it's often hard to corral colleagues on just about anything, Rep. Devin Nunes keeps the longhorns of a steer mounted inside his Capitol Hill office.

It's a gift from a cattle farmer in his Central California district and an ode to his previous career as a little-known cattle and dairy farmer.

Nunes still maintains his farm, but now the eight-term Republican chairman of the House Intelligence Committee is facing an unexpected stampede as he leads the House's investigation into Russia's meddling in the US election -- including any possible ties to top Trump campaign aides -- and faces calls from Democrats to step down from his post

At the heart of the sudden focus on Nunes is a bizarre trip to the White House

Nunes admitted Monday that he held a meeting on White House grounds the day before he revealed that the government could have incidentally collected Trump and his staffers' communications in its surveillance of foreign leaders and their staff.

Swirling questions -- including who is Nunes' source, who cleared him onto White House grounds and what documents he viewed there -- remain unanswered.

Meanwhile, Democrats -- and at least one Republican, Rep. Walter Jones of North Carolina -- are calling for Nunes to step aside in the Russia investigation.

Their argument is that Nunes -- who was a member of Trump's transition team, advising it on appointments -- is improperly providing political cover for Trump's unsubstantiated claim that Obama ordered a wiretap of his phone at Trump Tower

Still, Nunes' Republican colleagues have rushed to his defense.

"I have absolute faith in his personal integrity," said Oklahoma Rep. Tom Cole. "I think the fact that he was one of the first people to stand up and say, 'Look, I know the President thinks that President Obama ordered a wiretap, or has suspicions -- that's not the case.' I think that tells you he's certainly willing to call them the way he sees them."

Until the investigation started into potential ties between Trump advisers and Russian officials, Nunes was by no means a national name.

Now, though, he's among the most closely-watched figures in Congress. And the pressure that's come with the sudden change is showing.

Nunes started out as an open and available presence in the investigation -- readily taking questions from reporters for more than 30 minutes at a time, always stopping to answer questions. But his trip to the White House last week -- and the firestorm that has erupted since then -- has changed his demeanor greatly, with him running from questions at times.

Nunes, 43, is Portugese-American whose family hails from the Azores. He is married with three children.

His political career began with a successful run for the board of trustees at the College of the Sequoias, where he'd earned his associate's degree. Nunes later graduated from Cal Poly San Luis Obispo with a bachelor's degree in agricultural business and a master's degree in agriculture.

In 2001, he was tapped by President George W. Bush to be the California state director of the rural development program run by the Department of Agriculture. He left that post a year later to successfully run for his seat in the House, winning with 70% of the vote. He's been reelected seven times with at least 60% and sometimes over 70% of the vote — and even once unopposed — in a district that the nonpartisan Cook Political Report describes as leaning strongly Republican.

Nunes' GOP colleagues credit him with being in tune with the inner workings of the legislative branch.

"As a new guy, he was very helpful to me and helping me understand, 'Look man, this is a different ballgame and you know, something that you don't think is a slight at all, nor should be a slight, will be remembered six months down the road, when you're wondering why this guy isn't responding how you thought he would,'" said Indiana Rep. Todd Rokita. "So just stuff like that he is very sensitive too, very intuitive with, that was just very helpful to me."

Nunes is closely allied with another rural California lawmaker, House Majority Leader Kevin McCarthy, and was tight with former House Speaker John Boehner of Ohio.

However, he is not as close with current House Speaker Paul Ryan of Wisconsin. Ryan beat Nunes for the open chairmanship of the House Ways and Means Committee in 2014.

Prior to that, Nunes earned the ire of his Republican colleagues in 2013 after he blasted the government shutdown and called out other Republicans for supporting it.

"They have to be more than just a lemming. Because jumping to your death is not enough," he told the Washington Post in 2013. "You have this group saying somehow if you're not with them, you're with Obamacare. If you're not with their plan -- exactly what they want to do, you're with Obamacare. It's getting a little old."

His close ties with Boehner led to being picked in 2014 to head the House Intelligence Committee -- the role that led to his leadership of the Russia investigation.

When Ryan left the Ways and Means job to become speaker, Nunes considered another run to lead that committee, but wound up staying at the helm of the Intelligence Committee at Ryan's request.

Ryan was asked Tuesday if he knows Nunes' source for information he viewed at the White House and whether Nunes should recuse himself from the Russia investigation.

"No and no," the speaker said.