President Trump plans a European trip next week for a gathering of representatives of the world's largest economies — including those of allies such as Britain, Japan and Germany, and rivals such as China and Russia.

The high-profile meetings will reinforce the general sense Americans share of any president: He is the head of state, the face of the nation, the principal architect of U.S. foreign policy and our advocate in the counsels of global power.

Yet, in fact, the president makes and executes foreign policy not by himself but in a complex partnership with Congress. The role of Capitol Hill is easy to overlook, especially because Congress usually attracts far less attention in carrying out its part of the foreign policy process.

That is especially true when Congress is focused intensely on a high-value domestic issue such as the health care bill now before the Senate. It is rare for an international issue to hold center stage for long on the Hill, and most members look to other policy areas to make their mark and please their folks back home.

But on foreign policy, as with so many other things, the Trump Era is producing some unusual behavior. In just the month of June, Congress showed several signs of stepping out on the international front.

Senate Foreign Relations Committee Chairman Bob Corker, R-Tenn., on June 26 staked out a position on a dispute between several of Persian Gulf allies that was quite distinct from President Trump's expressions on Twitter regarding the same dispute. Corker even spoke of holding up arms sales to the region that the Trump administration has trumpeted as a success story.

Less than two weeks earlier, the Senate had passed a sanctions bill that included fresh punitive measures for Russia. These were on top of sanctions imposed by the Obama administration last winter in response to Russian meddling in the 2016 election campaign (and still earlier after Russia seized Crimea interfered in Eastern Ukraine).

What made this bill especially noteworthy was the near-unanimous vote for passage, and the language limiting the White House's authority to lift the sanctions on its own.

The House has yet to take up this legislation, and the president could veto it. Secretary of State Rex Tillerson has at least raised questions about it. But the near vote sent a "veto-proof" signal that could scarcely be missed.

All this is surprising for two reasons. First, the Republican Party controls both the executive and legislative branches and might be expected to be more in sync with itself. Second, Congress has generally followed a pattern of deferring to the executive on foreign policy — a pattern in place for decades.

Will the Trump administration see that inclination change? That question begs another: What is the role of the Congress in foreign policy supposed to be in the first place?

Sixty years ago, the constitutional scholar Edward Corwin described the Constitution's language on the subject as "an invitation to struggle for the privilege of directing American foreign policy."

The Constitution gave some of the authority to the executive and some to the legislative branch, with the overlapping areas left open for negotiation.

The founders knew well that this arrangement would require much coordination and give and take. And they knew that would be difficult. That's what Corwin meant about "struggle."

So the president was to be the military's commander-in-chief, but only the Congress had the power to declare war. Since World War II, the U.S. has fought in Korea, Vietnam, the Persian Gulf, Afghanistan and Iraq without war ever being declared. Presidents have found alternative ways to get our armed forces committed and also to get Congress to support them.

The president picks his own people to head the State Department and the Defense Department and a variety of other agencies to conduct the U.S. foreign policy. But the Senate can block some of those appointments, including the most important.

The Congress is also solely empowered to appropriate the actual funds for all these functions. And it has separate committees that authorize the various departments, setting out rules and guidelines for those departments that are enormously important to their internal business.

Congress also votes on trade deals such as NAFTA and international treaties such as the Iran nuclear deal in 2015.

So it would seem the Congress has many levers to work (or not work) that matter to the machinery. Yet as a practical matter, the modern Congress has usually chosen to cooperate or defer to the executive.

Any vote on matters as thankless as overseas military commitments is seen as more likely to harm than help a congressional career. More typically, Congress lets the president take the lead, and lets him take the heat when things go wrong.

Even when control was split between the parties, Congress has sought few outright confrontations on these issues. And presidents have found ways around Congress, as when the Iran deal survived a disapproval measure in the Senate, thanks to a special procedure that allowed Democrats to prevail by filibustering a measure to kill the deal.

What seemed a textbook case for Congress to assert itself became instead a demonstration of how easily Congress can be thwarted.

This is not a terribly new development. Presidents have been emerging as the dominant actor in our foreign affairs for more than a century. Strong personalities such as Teddy Roosevelt, Woodrow Wilson and Franklin Roosevelt dominated the first half of the 1900s.

Since World War II, the realities of rival world powers wielding nuclear weapons have further empowered the president. More recently, the rise of the Internet and instant communications have further exaggerated the advantages of the person at the head of the military and the federal executive structure.

There have been times of pushback. Congress passed the War Powers Act in 1973 in the wake of the Vietnam War and at a time when the presidency was weakened by scandal. Congress also staged extensive debates before approving the use of force against Iraq in 1991 and again in 2002.

More than a few members came to regret the second of these votes quite a bit. Partly as a consequence, efforts by President Barack Obama to get an authorization to fight ISIS were largely ignored by congressional leaders.

Obama relied instead on a separate authorization passed to fight a "global war on terror" after the attacks of Sept. 11, 2001.

And once again, Congress let that go, preferring not to struggle.

Now we are seeing the first divergence of powerful Republicans from the White House line on foreign affairs. There could be further examples ahead regarding Russia and China, North and South Korea, the Philippines, Iran, Iraq, Syria and NATO — just to name a few.

The foreign policy thrust of the White House is itself a struggle between more traditional Republicans and advocates of "America First" nationalism. Depending on who gains the upper hand internally, the Trump administration policy could enjoy the usual degree of deference from this Republican Congress or it could experience the kind of turbulence not seen since the Vietnam War a generation ago.

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