An Israeli ground invasion of the Hamas-ruled Gaza Strip is no longer a question of “if” but “when.” Approximately 360,000 Israeli reservists have been mobilized over the last week, with most of the troops stationed close to the Israel-Gaza border fence. Israel’s evacuation order for the northern section of Gaza, where about 1 million Palestinians live, is still in effect. The Israel Defense Forces (IDF) conducted limited probing attacks inside Gaza over the weekend, and Israeli airstrikes have continued nonstop.

As bad as the war between Israel and Hamas is, it could get even worse if the fighting expanded. Some U.S. politicians and pundits are perfectly fine with the prospect and even recommended that the Biden administration take the fight directly to Iran, Hamas’ main external backer.

Senator Lindsey Graham (R-S.C.), an arch Iran hawk, has used several television appearances to press for war against Tehran. On Oct. 15, the senator stated the U.S. should “knock Iran out of the oil business” if Hezbollah, its proxy in southern Lebanon, entered the conflict. Marc Thiessen, a Washington Post columnist and a former speechwriter in the George W. Bush administration, strongly urged President Joe Biden to set a red line to Iran.

The justifiable outrage about what Hamas has done to innocent civilians is clearly spreading to the terrorist group’s patrons. Emotion, however, is a terrible ingredient for good policy. Pundits are wholly unaccountable and have the luxury of not worrying about the consequences of their recommendations; policymakers, in contrast, have weighty responsibility on their shoulders and need to closely weigh the costs and benefits of every plausible scenario.

First, we should be clear about one thing: just because Tehran is a sponsor of Hamas doesn’t necessarily mean it was operationally involved in the terror group’s rampage in Israel. This isn’t about making any excuses for Iran, who after all is the world’s preeminent state sponsor of terrorism, but rather to point out a simple fact. Based on the information we know right now, there is no intelligence supporting the conclusion that the Iranians were specifically aware of what Hamas was planning. The U.S. intelligence community has acquired information suggesting Iran was surprised by Hamas’ operation. Secretary of State Antony Blinken publicly stated, “We don’t have direct evidence that Iran was involved in the attack, either in planning it or carrying it out.” Israeli intelligence concurred with this judgment.

That assessment may change over time. But at this moment, Iran’s link to the worst terrorist attack Israel has ever experienced is murky at best. One would think, or at least hope, the U.S. wouldn’t take the country to war on incomplete or contradictory intelligence. After all, the U.S. did exactly that in Iraq two decades ago and the result was an unmitigated disaster for U.S. power, influence, and credibility.

In an ideal world, the military option against Iran would be off the table based on this fact alone. Unfortunately, we don’t live in an ideal world. Some, like John Bolton, former President Donald Trump‘s national security adviser, have long advocated for the use of U.S. military force against Tehran, and use every opportunity to buttress their argument for military action.

It’s telling, however, that these same proponents fail to seriously consider the costs attached to such an operation. And the costs are so exceedingly high that whatever benefits may arise out of a military campaign are practically irrelevant. This is true even more so today, when Israel has its hands full planning and likely executing a large-scale ground offensive in Gaza that could last months.

Any attack against Iran would turn the 30,000 U.S. troops stationed throughout the Middle East into prime targets for Iranian reprisal. We know this because American troops have been targeted by the Iranians before, not only through proxies in Iraq and Syria, but directly. After the Trump administration assassinated Qassem Soleimani, a top commander of the Islamic Revolutionary Guard Corps (IRGC), the Iranians sent a fuselage of ballistic missiles toward several U.S. bases in response. Fortunately, no American servicemembers were killed in those exchanges. But the entire episode served as a warning to both countries: even a limited exchange of fire between the two countries could upend the Middle East, bloody both sides, and escalate without warning.

While there is no doubt the Iranians would prefer to avoid a conventional war with the U.S., Tehran isn’t afraid to retaliate if it’s hit. Iran’s capacity to do so has only gotten stronger since Soleimani’s assassination. While Tehran may not have any allies in the region (even Syria’s Bashar al-Assad can’t be considered an ally in the traditional sense of the word), the IRGC has built up and nurtured a system of non-state proxy groups that could be called upon in the event of a U.S. military campaign. The roughly 3,500 U.S. troops in Iraq and Syria would be sitting ducks, having to dodge rocket fire and drone attacks from Iran’s proxy network to a greater extent than they already are. American casualties would compel the White House to send even more U.S. military power into the region for force-protection purposes, which in turn would provide Iran and the litany of militias under its thumb with even more targets. One can’t overstate just how quickly a situation like this could spiral into a full-fledged war between the U.S. and Iran, which both have sought to avoid.

Israel, too, would be in for a very difficult period. The IDF is an extremely capable force, yet it has never been tested on two fronts simultaneously. Although the missile attacks and airstrikes between Israel and Hezbollah over the past several days are a concern, those engagements have been limited thus far. This would no longer be the case if U.S. bomber aircraft dropped their payloads in Iran. It’s inconceivable that Hezbollah would be restrained in such a scenario. This would not only be terrible for Israelis who live in the north but also for those in Tel Aviv; Hezbollah’s missile arsenal can reach Israel’s major population centers. Unlike the rocket arsenals of Hamas and Palestinian Islamic Jihad, Hezbollah’s missile capability includes at least some with precision-guided technology. Casualties in Israel would be immense.

Taking the fight to Iran is the last thing the U.S. should do. It was a terrible idea when it was proposed in the past, and it’s a terrible idea now.

Daniel R. DePetris is a fellow at Defense Priorities and a syndicated foreign affairs columnist at the Chicago Tribune.

The views expressed in this article are the writer’s own.