Before they were allies, they were campaign-trail foes.

Yet, since taking the gavel of the influential Ways and Means Committee, Chairman Paul Ryan has emerged as President Obama's most convincing messenger on Capitol Hill on behalf of a free-trade agreement that would be a big boost to the president's legislative legacy.

The House could vote on Trade Promotion Authority, also known as "fast track," as early as this week. The legislation would limit Congress to an up-or-down vote on future trade deals negotiated by the president. If it passes, it will be a kind of graduation moment for Ryan, the first major legislative accomplishment since he left the Budget Committee. Unlike his visionary budget documents that made him a sensation in conservative circles, however, trade puts Ryan on the same side as a president conservatives distrust and tests the relationships he has carefully built with those in the far right of his party.

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"The fact that the president is involved in the process makes it more difficult for any Republican, compared to simply putting together our own budget that the president does not have to sign," House Financial Services Committee Chairman Jeb Hensarling says of Ryan's trade push.

Since taking over the House Ways and Means Committee six months ago, Ryan has been engaged in mapping out the way forward on a trade bill that is a key priority for Obama. But Ryan's calculation, and the message he gives to Republicans, is that it is just as important to the GOP's own economic and electoral success.

"If Republicans derail trade, we add to the narrative that America is on decline, which is now uniquely tied to Obama's policies—policies we disagree with profoundly as Republicans," Ryan told National Journal.

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Even before Republican leaders began whipping the bill weeks ago, Ryan was undertaking his own member-tracking operation. He held dozens of education seminars. He invited conservatives to meet with him privately. He listened to concerns and made his pitch that trade was an essential part of growing the economy. This week alone, Ryan has met with 20 members of his party in one-on-one meetings. While he acknowledges he's working on the same side as the president, Ryan underscores that the trade bill he is pushing will outlast this president, and that trade deals are fundamentally conservative.

"If the name Obama was nowhere to be seen in this, it would be fine for most people," Ryan says. "We believe in free trade. That is one of our party's primary principles."

As the vote on TPA approaches, there is increasing pressure on Ryan and Republican leadership to deliver votes from conservatives who are skeptical of supporting anything that boosts Obama. While the White House has its own whip operation, it's been difficult for administration officials to garner the 25 to 30 Democratic votes they will need to deliver. Several GOP aides have expressed frustration that the administration isn't holding up its side of the bargain. Many have blamed the administration for leaning on members it had—up to this point—failed to build relationships with. And to make things more difficult, trade unions have stepped up their lobbying efforts and Democratic leaders are staying on the sidelines.

(RELATED: With Trade Vote Looming, Hoyer Stays On the Fence

But those within the Republican whip operation say all of the turmoil on the Democratic side has hardly distracted Ryan. Instead, it has emboldened him to double down on his engagement strategy. Republicans say the strategy has been far more involved than the typical whip operation, as leaders reach out to state movers and shakers in agriculture, business, and manufacturing to influence wavering members. Business Roundtable spokesman Kevin Madden said his group has spent in the "seven figures" on advertising in 160 districts.

"Each pitch has been tailored to each individual," says Rep. Tom Cole, who is on the whip team and is supporting TPA. "We are trying to move people on a one-on-one basis. This is very unusual that we are going to this kind of effort."

But Cole says Ryan continues to be the single most convincing member on the issue.

"He has an intellectual credibility that no other member matches. He brings enormous prestige to this," Cole says. "No one else serving on the floor has been the candidate for vice president of the United States, and throughout the entire Republican coalition, he really has been the architect of our thinking on everything from entitlement reform to financial policy to trade."

(RELATED: The Trade Paradox

Ryan earned his wonkish wunderkind persona early after arriving on Capitol Hill at the age of 28. With his budgets, he helped define his party's vision. And, after serving as the party's vice presidential candidate in 2012, he returned to the House of Representatives with an even higher-profile status. But Ryan has been tested before. When he forged ahead with a bipartisan budget compromise alongside Democratic Sen. Patty Murray, he got flack from outside groups and conservative pundits who viewed the deal as Republican capitulation. Sen. Marco Rubio called it "irresponsible."

But instead of lashing out and saying conservative groups had "lost all credibility," as House Speaker John Boehner did, Ryan called the outside groups "important elements of our conservative family."

And, in his quest to secure votes for TPA, Ryan has relied on the contacts he has forged with outside groups like Heritage and Club for Growth. They wield considerable power over conservative members and could be key to Ryan passing TPA. Ryan has been working to ensure that neither group scores fast-track negatively.

Club for Growth President David McIntosh says that while his group supports TPA, it has concerns about a currency-manipulation measure that is tied to it. The Club would also like to see Boehner promise to let the Export-Import Bank expire as part of the trade negotiation. Yet McIntosh said his group—which supports the underlying free-trade principles—is still leaning toward remaining neutral on the bill if those demands are not met. That decision, he says, has a lot to do with Paul Ryan.

"People trust him and know that when he says something, he is not telling someone else something else. He has a lot of integrity," McIntosh says. "He has the relationship with us that we will certainly listen to him and respect his assessment."

Americans for Tax Reform founder and president Grover Norquist, who supports TPA, said he's been impressed to see Ryan's intensive reach-out operation.

"Ryan spends more face time with more members than any other Republican," Norquist says.

Norquist is doing his own outreach as well on Capitol Hill, and ATR is making calls in 40 districts to encourage voters to contact their members of Congress.

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