Two conservative Republican senators, two potential paths to the White House. Cruz, who during nine months in office has made at least a half-dozen trips to early-primary states, is riding the wave. Rubio, whose last visit to an early-voting state was Iowa in November, is playing the long game. His allies dismiss the early polling and argue that letting Cruz be the poster boy for the government shutdown might not be such a bad idea.

Sen. Jeff Flake of Arizona, a Republican who partnered with Rubio on immigration reform, said Thursday: "You're looking at a snapshot of a couple of days of something. I always felt that Sen. Rubio will benefit from his serious work on a substantive issue, and I still think he will."

Flake added, "Winning the presidency is about winning a general, not just a primary."

Asked why he hasn't been more outspoken this week, Rubio said he's "more than happy to share his views" with House Republicans that the health care law will damage the economy and Democrats are to blame for the budget impasse. Rubio said he supports the effort by House Republicans to pass short-term funding for veterans, the National Park Service, and the D.C. government.

Rubio joined Cruz during his marathon speech on the Senate floor to show his support.

"People know where I stand on the issue," Rubio said Thursday after leaving a Senate Foreign Relations Committee hearing on Iran's nuclear program. "There's not legislative action, there isn't anything happening, there's nothing to speak out on."

That hasn't stopped other prominent conservative Republicans like Cruz, Sen. Mike Lee of Utah, and Sen. Rand Paul of Kentucky from holding court with reporters day after day. Paul hosted a "bipartisan coffee" Thursday on the steps of the Senate that attracted more than a couple dozen reporters and only a handful of elected officials.

"The more you pick a fight with Washington, the better you look out in the country," said Republican consultant David Kochel, who ran Mitt Romney's winning campaign in the 2012 Iowa caucus. "Sen. Cruz has got a hot hand right now with a certain part of the grassroots that is really charged up, but we still have to wait for this to play out. I think in the end Sen. Rubio will get credit from the part of the party that's more interested in making sure things work than these symbolic protests."

American Conservative Union Chairman Al Cardenas, who's known Rubio for more than a decade, said his style is to be more collegial, while Cruz seems to relish confrontations with fellow Republicans worried about the negative fallout from the shutdown. Rubio's relationships with other senators could be valuable if he decides to run for national office.

"You will never see Rubio taking on his colleagues head on," Cardenas said. "That's not a place of comfort for him."