A sea change in the composition of the Congress is always taken to have profound consequences for American foreign policy. Those expectations usually prove exaggerated. The broad consensus on the basic premises of the country's external relations is too strong to permit stark confrontations. Moreover, there currently are no earth-shaking issues dividing the country -- as Vietnam did in the 1960s and 1970s. This year, international questions figured hardly at all in the election. Republicans did harp on a few stories that added to their narrative of an incompetent White House (e.g. Benghazi), but that was about it.
The Republicans are not attached to any particular philosophy or committed to any particular strategy or doctrine. They do try to foster the image of being tougher in defending American national interests and more attentive to security threats. That is largely verbiage, though. The Obama administration pretty much has followed in the footsteps of its Bush predecessor, especially in regard to prosecution of the War on Terror which is the one issue that has a grip on the American body politic. On the outstanding questions of the moment in the Middle East, Republican leaders are as confused and uncertain as is the White House. Indeed, there also are significant differences among prominent Republican Senators as to what tack to take. Rand Paul, a likely candidate for the party's presidential nomination, vocally opposes expanded military intervention and even has become the leading critic of spying and surveillance abuses by the NSA and CIA. That is a minority view, but it is indicative of a current in the electorate that is disaffected by the United States' serial, failed interventions. Senators John McCain and Lindsey Graham may want to bomb as soon as you see the whites of the eyes of forces hostile to the United States; they do not speak for the Congressional Party as a whole, though.
The Republican priority will remain the obstruction and embarrassment of Barack Obama at every turn with an eye on the 2016 elections. Their aim to build a new Republican dynasty on the rubble of Obama's ill-starred eight-year tenure. Criticizing his foreign policy moves is just another step in that direction. There are a handful of items on the foreign policy agenda that could be affected by the turnover on Capitol Hill.
On Iran:
Much depends on whether the nuclear negotiations lead to an agreement before the new Senate convenes in January. Since Obama already has said that he will not present a treaty to the Senate for ratification, an agreement before January would not necessarily be jeopardized by Republican opposition. However, the shift in the Senate could accentuate two other problematic aspects of the situation. One, there could be a renewed move to pass legislation which prevents the lifting of some economic sanctions and/or imposes other restrictions on normalizing relations. Remember, there were Democratic sponsors of the earlier effort (e.g, Menendez of New Jersey was the leader). Would it take 60 votes to get the legislation through or just 50? Most likely 50 since the Democrats are far less disciplined than the Republicans, are not unified on the issue and will make no particular effort to protect the President. Two, the Iranians are already uneasy about an agreement wherein the United States' pledges to ease sanctions depend on the voluntary action of the White House rather than being conferred legally in a Treaty. Their apprehensions can only deepen with Republicans in control of Congress and with a good shot at the Presidency in 2016. Iran could retaliate, of course, by voiding their own commitments - but obviously don't want to be put in that position.
TPP and TTIP, the wide-ranging trade liberalization treaties in advanced stages of negotiation with European and Pacific commercial partners:
This is the great underreported story. The draft proposals are the most radical move in the direction of an unregulated world market place in history. In effect, states would relinquish a large slice of their sovereign authority to set standards in a variety of areas: environment, working conditions, etc. That authority would not be transferred to a supranational authority a la the European Union but to the free market itself. In effect, the authority to control would cease to exist. The envisaged appeal panels would be required to treat states and private businesses on an equal footing. In today's environment, that entails a bias in favor of private parties. This conforms perfectly with the Republican philosophy which is shaped by business interests. Such legislative opposition as exists has come from some progressive Democrats. On this score, Obama aligns himself with the Republicans. So we might expect to see a more energetic American push in the negotiations and a quick move to get ratification by the Senate.
Russia:
There will be little practical effect. Obama has been pursuing a hardline and is reticent about engaging Putin on Ukraine in the face of the latter's militant actions. The Republicans, though, will try to get a reinforcement of the current tough Obama line and prevent any future engagement with Putin by painting Putin/Russia as a dangerous enemy who must be quarantined and contained a la the Cold War. Already, the bipartisan theme heard around Washington is that there can be no serious business with Russia until Putin goes. Frictions with Germany and much of Western Europe, therefore, will be furthered strained.
Climate Change?:
Forget about it. The Republicans will undercut every serious move to achieve substantial cuts in emissions that lead to global warming. This attitude conforms with their anti-government dogma as well the rejectionists who will not acknowledge that a problem exists until they find seaweed in their breakfast-of-champions cereal bowl. After all, the Republican Party is the political instrument of American business and finance.