Of course Trump and the GOP can try all sorts of voter suppression, which is what they're doing now.
Claiming this strike on Iran is an attempt to suspend US elections is exactly as ridiculous as claiming the last round of strikes on Iran, or the Maduro raid, or any of Trump's other previous military boondoggles were attempts to suspend US elections.
Yes we can? Is there any provision in the US Constitution that allows delay of election because of war? We have had elections during most of our recent wars (Iraq, Vietnam, Korea, Afghanistan).
Trump could definitely try. Or pull an emergency card out of his ass. But it doesn't mean there is any provision for cancelling elections because of this 'war' with Iran (which they aren't even calling a war, but a "special combat operation" to get around congress having the war powers)