Using the cover of helping Syrian President Bashar al-Assad against domestic insurgents, Tehran now has stationed an estimated 125,000 troops in that country, outnumbering the Syrian army, and enhanced by Russian forces. This is in addition to thousands of Iranian militia allegedly "helping" Iraq forces extinguish ISIS threats there.
Ambassador Nikki Haley outlined last week how Iran is flouting United Nations resolutions by supporting and arming Yemen's Houthi rebels, who recently fired an Iranian missile into Saudi Arabia.
Under pressure from U.S.-advised troops and Iranian and Russian attacks, ISIS has effectively declined as an organized military threat, leaving Iranian and allied Hezbollah forces with time and motivation to make other mischief.
White House National Security Adviser H.R. McMaster's team is currently developing a new post-ISIS strategy focusing on neutralizing or containing the looming threat of Iran to Israel and U.S. forces.
In his national security outline this week President Donald Trump noted the global balance of power has shifted in recent years in ways adverse to U.S. interests. He focused on Russia and China in this congressionally-mandated statement, adding realistically, "Whether we like it or not, we are engaged in a new era of competition."
But Iran is likely to be a major policy target in the new year when the McMaster strategy is completed. With American troops still fighting in Afghanistan now for the 17th year, presenting a case for confronting Iran anew is likely to take considerable public education and selling, short of a direct attack on Israel or American troops.
Meanwhile, Defense Secretary James Mattis has indicated the 2,000 special operators stationed in Syria are not going anywhere soon in order to stymie any ISIS rebirth. But this raises the possibility of armed encounters with Iran's nearby forces.
Already, U.S. planes have downed two armed Iranian drones. Israeli planes regularly bomb Hezbollah convoys in Syria. And intelligence reports say Iran is building a missile base in northwest Syria.
"What we face," McMaster said recently, "is the prospect of Iran having a proxy army on the borders of Israel." That's a more imminent threat to the closest U.S. Middle Eastern ally than the longstanding -- and remaining concern -- about Iranian missiles traveling the 600 miles to "erase" Israel, as Tehran has threatened.
President Barack Obama preferred ineffective words, red lines and sanctions against the Syrian regime. He ignored Iran's troop buildup in Syria in favor of negotiating his much-coveted nuclear weapons agreement with Tehran. Trump has denounced that agreement as "incomprehensibly bad" and certified to Congress this fall that Iran is not living up to the spirit of the pact.
With Trump already facing down a rapidly-developing nuclear threat from North Korea, the stakes with Iran are high and growing. Such confrontations are likely to figure in the current budget debate over the GOP's enhanced defense appropriation desires versus the domestic spending priorities of Democrats.
No U.N. resolutions, sanctions or words have halted Iran's expansionist ambitions. Like Russia, Iran has cycled much of its armed forces through years of Syrian fighting, giving them real-life regular army training under Russians and actual combat experience for whatever Iran's future military plans might be.
The nonpartisan Institute for the Study of War reported earlier this year that "Iranian military cooperation with Russia in Syria is dramatically increasing Tehran's ability to plan and conduct complex conventional operationsâ€¦ (and) is transforming its military to be able to conduct quasi-conventional warfare hundreds of miles from its borders. This capability, which very few states in the world have, will fundamentally alter the strategic calculus and balance of power within the Middle East."
Washington is consumed this month with passing the tax bill and a continuing spending resolution, both of which have been languishing all fall. And, of course, there's a half-month recess to enjoy.
But the volatile Iranian problem, like that annual arrival of post-holiday credit-card bills, is likely to come due early in 2018.
McClatchy Washington Bureau