If President Trump wants to get his nominee for U.S. Trade Representative confirmed, he'll have to do it without the votes of Sens. Ben Sasse, R-Neb., and John McCain, R-Ariz. It remains to be seen how many other Republicans will be willing to buck Trump and his protectionist sympathies on the issue of trade.

Sasse and McCain sent a letter to Trump's nominee, Robert Lighthizer, announcing that they will be opposing him, and giving their reasons why.

"A constant theme throughout your confirmation process has been your failure to grasp the importance of protecting agriculture in trade negotiations," the two noted. "Your meeting with one of us (Senator Sasse) did nothing to disabuse of us this notion. America needs a USTR who will effectively defend agriculture during trade negotiations and fight to expand agricultural export markets, not let America's farmers and ranchers become collateral damage in a trade war."

Sasse and McCain also called the Trump administration's position on trade "incoherent and inconsistent," and pointed to Lighthizer's outspoken opposition to NAFTA as an obstacle to his winning their support:

"America deserves a USTR who will renegotiate NAFTA in order to build on its successes, not as a pretext for unraveling it. Mexico and Canada are two of our largest export markets and the free movement of goods is essential to the growth of our national economy. For example, Mexico is Arizona's number one trading partner, accounting for 40 percent of the State's exports to foreign markets. This is due to the free trade policies in NAFTA that create fewer trade barriers with Canada and Mexico, which makes it easier for Americans to make a living and provide for their families. Further, according to the Nebraska Farm Bureau, a withdraw from NAFTA could cost Nebraska farmers and ranchers more than $2.6 billion per year in agricultural exports. Increasing trade barriers with Canada and Mexico, and risking a trade war, only hurts American families and small businesses.

Congress passed a provision in the recent omnibus spending bill that grants Lighthizer a waiver to serve as USTR, a requirement for him because as an attorney he represented foreign governments long ago. Lighthizer will need Democratic support in the Senate if he loses the votes of more than two Republicans, although that might not be a problem — he was voted unanimously out of the Senate Finance Committee last month.

Senate Majority Leader Mitch McConnell, R-Ky., filed a cloture motion on Lighthizer's nomination earlier this week.