Russia’s actions in Ukraine, as well as its military build-up and threatening words and behavior in the Baltic Sea region, show that we have not yet fully communicated to the Kremlin that it should back off. …

From our vantage point, we see five priorities for NATO:

• The deployment of serious forces by other NATO countries in the Baltic states and Poland….

• A standing defense plan. It doesn’t make sense for NATO to try to defend the Baltic states or Poland in isolation. If Russia attacks NATO, it attacks all NATO members. And it should therefore fear a response from all NATO members against all its territory. There should be no room in Mr. Putin’s strategic calculus for a limited, low-risk operation in the Baltic region. Any provocation in our region should mean the instant and determined deployment of the alliance’s military, economic, political and other assets.

• Political preauthorization. When the air-policing mission scrambles from its bases in Estonia and Lithuania, it doesn’t wait for a meeting of the North Atlantic Council, NATO’s main decision-making body. It responds to military necessity. We need the same with regard to other NATO forces in our region, whether they are dealing with provocations on air, sea, land or over the Internet.

• NATO needs to move beyond its old war-fighting doctrines. A strong conventional (and nuclear) posture will deter Russian military might, but our countries face other threats too. We need tighter cooperation on dealing with Russian propaganda, subversion, espionage, energy blackmail and political corruption….

• The Warsaw summit should mark an intensified partnership with Sweden and Finland. We strongly hope that these two friends will join the alliance soon. But there remains huge scope for intensified security cooperation. NATO shouldn’t hesitate to change any rules that hamper this. We cannot defend the Baltic Sea region’s security without the fullest possible participation of the countries that have stakes in it.

Mr. Sikorski is former foreign minister of Poland. Ms. Vike-Freiberga is the former president of Latvia.

Image: NATO Exercise Noble Jump, June 18, 2015 (photo: Erik Morren/German/Netherlands Corps)