Gordon Humphrey, a Republican from New Hampshire, was a member of the U.S. Senate from 1979 to 1990 and co-chaired the Congressional Task Force on Afghanistan.

Since the White House has shown that it won’t take the lead in thwarting Russian President Vladimir Putin’s plan to permanently divide Ukraine , Congress should assert its role as a co-equal branch of government. The change in the Senate leadership in the next Congress will make that easier, but the Senate should act now, not wait until January.

Further delay in supplying Ukraine with defensive weapons will give Putin time to consolidate his position and lay plans for further aggression. Delay also raises the prospect of an even more serious challenge — this time to NATO in the Baltic States, where Putin is already inventing pretexts to make trouble.

Sens. Carl Levin (D-Mich.) and Robert Menendez (D-N.J.) have led the way in arguing for providing defensive weapons. Levin, the chairman of the Armed Services Committee, called for taking the step in a July floor speech : “As part of [our] effort we should provide Ukraine with defensive weapons — such as antitank weapons — that can help Ukraine reclaim its territory and deter Russian aggression, without being needlessly provocative to the Russians.” Menendez, the chairman of the Foreign Relations Committee, put it plainly in a September NPR interview: “If a tank is coming at you and you’re firing with a peashooter, you’re not going to be able to stop that tank.”

But senators, even the most powerful, cannot prevail on an issue like this one when acting independently. Only a large, well-staffed, bipartisan team can get the job done. What’s needed is a bipartisan Senate task force on Ukraine.

At present, I count 47 senators — Democrats and Republicans — who are on record supporting lethal defensive weapons for Ukraine. That is a high starting number, given the profound nature of the question and the opposition of President Obama. Few of the remaining 53 have spoken publicly on the issue, but surely among them are enough to comprise a large majority when added to the 47. And it’s likely that newly elected Republican senators will be more supportive of defensive weapons for Ukraine, given that about two-thirds of current backers are Republican; certainly, the likely replacement of Harry Reid by Mitch McConnell as majority leader ensures the Senate will chart its own course, not that of the White House. By bringing their numbers to bear and working in concert, supporters will be much better positioned to prevail by assertively advancing the Menendez weapons bill and companion appropriations and using parliamentary leverage when necessary.

There is precedent for this. In the 1980s, Democratic and Republican senators formed a task force on Afghanistan to deal with executive resistance to sending modern weapons to the fighters taking on the Soviet army. Claiborne Pell (D-R.I.), the chairman of the Senate Foreign Relations Committee, and Daniel Patrick Moynihan (D-N.Y.) were among its active members, as was one of the Senate’s most senior current members, Orrin Hatch (R-Utah).

The task force on Afghanistan induced the executive branch to greatly increase humanitarian assistance and, most important, supply modern defensive weapons, including antiaircraft weapons, to the Afghans fighting the Soviet Army. The weapons changed the calculus in Moscow, and ultimately the Soviets withdrew. Senators should reflect on that outcome and the means used to achieve it. Then they should apply the lesson today. Of course, we should bear in mind that when the Soviets withdrew from Afghanistan, the United States also departed, leaving a vacuum with unfortunate consequences. We must not repeat that mistake in our support of Ukraine. Support must be long-term, as was our support of Western Europe following World War II.

To succeed, senators supporting lethal defensive weapons must have a full team on the field every day, not just a few superstars who speak out now and then. They need a bipartisan Senate task force on Ukraine, backed up by adequate staff constantly at work.

Congress can have the last word. The Senate should take the lead. Until it does, the White House will continue to win by default.