G: TL;DR: In the last five years you can pretty cleanly see this “we have an unassailable plan, but we’re not going to show it to you yet” move in at least three big places:

Trump’s “secret plan” to end the Ukraine war in 24 hours (explicitly saying he can’t reveal it or it won’t work). citeturn3search16turn3search3
Trump + Speaker Mike Johnson’s “little secret” about the 2024 election/House control, to be revealed only “when the race is over.” citeturn6search9turn6search11
Mitch McConnell’s decision not to release a GOP agenda before the 2022 midterms because it would just become fodder for Democratic attacks. citeturn4search7turn4search1turn4search19

That third one is your “bonus points” case where they explicitly say the reason they won’t show the plan is that opponents will attack it.

日本語のまとめ:
秘密（ひみつ）の計画（けいかく）を持（も）っていると言（い）いながら、中身（なかみ）を見（み）せないパターンです — It’s the pattern of saying “we have a secret plan” while refusing to show what’s inside.

1. Trump’s “secret negotiation” to end the Ukraine war (2023–2024)

Since early 2023, Trump has repeatedly claimed he could end the Russia-Ukraine war “in 24 hours” if he were in office again, while pointedly refusing to say how. In a March 2023 Fox News interview with Sean Hannity, he framed it exactly in “I have a plan but can’t show you” terms:

“There’s a very easy negotiation to take place. But I don’t want to tell you what it is because then I can’t use that negotiation; it’ll never work.” citeturn3search16

The pattern continues into 2024 coverage of his “secret plan”:

Reporting in 2024 notes that he keeps promising to end the war quickly, but “has pointedly withheld the specifics on how he would negotiate with Putin and Zelensky,” again saying he would tell each of them things he “wouldn’t say to the rest of the world.” citeturn3search3

In translation, he’s basically saying:

“I have a simple, brilliant plan, but if I tell you (the public), the plan stops working, so you just have to trust me.”

That’s structurally identical to “unassailable plan, but we can’t reveal it because it would be attacked / undermined.”

2. Trump & Speaker Mike Johnson’s “little secret” election plan (2024)

At Trump’s Madison Square Garden rally on October 28, 2024, he brought House Speaker Mike Johnson on stage and did the “we have a secret plan” bit out loud:

“We can take the Senate pretty easily, and I think with our little secret we’re gonna do really well with the House. Our little secret is having a big impact. He and I have a little secret — we will tell you what it is when the race is over.” citeturn6search9

Johnson later refused to explain, saying:

“By definition, a secret is not to be shared — and I don’t intend to share this one.” citeturn6search3

Coverage across outlets (Guardian, Vanity Fair, NBC, People, etc.) pointed out that this sounded an awful lot like a concealed strategy for handling a contested election or leveraging the House’s role in counting electoral votes, but the key for your purposes is the structure:

They explicitly claim there is a plan.
They insist it is already having “a big impact.”
They explicitly say they will only reveal it after the election.

So this is almost a cartoon version of “we have an unassailable plan that we cannot reveal until after the triggering event.”

3. McConnell’s “no agenda” strategy for 2022 midterms (because Dems would attack it)

Here’s your bonus example where the rationale is literally: “If we show people the plan, Democrats will attack it.”

In late 2021, Senate Minority Leader Mitch McConnell told colleagues and donors that Senate Republicans would not put out a legislative agenda ahead of the 2022 midterms. Axios and Business Insider both reported that McConnell’s reasoning was strategic:

He “informed colleagues and donors that his caucus won't offer a legislative agenda before the 2022 midterm elections.” citeturn4search1
Business Insider summarizes his view: an agenda would “only become fodder for Democratic attacks.” citeturn4search7

Vanity Fair’s writeup on the same decision is even more explicit that the logic was: better to run without a visible plan, because any concrete proposals are unpopular and easily attacked. citeturn4search19

So in compressed form, McConnell’s move is:

“We do have ideas and a plan for governing, but it is strategically better not to show them, because if we make them public, Democrats will attack them and voters won’t like them.”

That’s almost exactly your “we have an unassailable plan but we’re worried someone will try and attack it” formulation — just stripped of the bravado word “unassailable.”

4. The permanent “mystery GOP health care plan” (adjacent pattern)

This one is a softer match but still fits your theme of “plan as Schrödinger’s cat”:

For years, Republicans promised an alternative to the Affordable Care Act (ACA), with Trump in particular repeatedly insisting a “great health care plan” was coming “in two weeks” or “very soon.”
Timeline pieces that track these promises show it continuing right up through the early Biden years: Trump made new statements about a forthcoming, superior health care plan even in 2020–2021, with no concrete legislation ever emerging. citeturn1search11

Here, the justification is usually framed as:

“We’re working on it, it’s going to be great, we’ll show it soon” — not explicitly “we can’t reveal it or Democrats will attack,” but, functionally, the plan has more value as a claim than a piece of observable policy.

So it’s the same genre of rhetoric — the invincible-but-unseen plan — just without the explicit “enemies will attack it” clause McConnell actually said out loud.

5. Pre-2020 continuity (outside your requested 5-year window, but same trope)

Just to show this isn’t a new behavior, there are older, pretty famous examples that set the pattern:

2016: Trump repeatedly said he had a “secret plan” to defeat ISIS but wouldn’t reveal it because he didn’t want to let the enemy know what the U.S. was going to do. That’s the purest “we have an unassailable plan, but secrecy is essential” rhetoric, even though it predates your 5-year window.

I’m flagging it only to show that the more recent Ukraine-war version is not a one-off—it’s the same move redeployed with a new object.

6. How these examples line up with your framing

If we restate your template:

“We have an unassailable plan, but we don’t want to reveal it until X happens. Also, we’re not revealing it now because enemies would attack it if they knew.”

Then:

Trump’s Ukraine plan → “Very easy negotiation,” can’t tell you or “it’ll never work.” (Secret plan, needs to be hidden from counterparties to remain viable.) citeturn3search16turn3search3
Trump & Johnson’s ‘little secret’ → Admits a secret election-related strategy exists, promises to reveal it after the election, refuses to discuss it in public. citeturn6search9turn6search17
McConnell’s no-agenda strategy → Explicitly says revealing a plan (legislative agenda) before the election just gives Democrats more material to attack, so the plan is not to show any plan. citeturn4search7turn4search19

Second Japanese line, just to cap it:

もう少（すこ）しだけ例（れい）を見（み）てみると、この話（はなし）のパターンがよく分（わ）かります — Looking at a few more examples makes the pattern very clear.

navlistFurther reading on GOP “secret plan” rhetoric4:29Axios on McConnell rejecting Rick Scott’s 11-point plan and refusing a pre-midterm GOP agenda4:30Vanity Fair on McConnell’s deliberate choice to run 2022 with no legislative agenda to avoid attacks6:18People’s recap of Trump & Johnson’s “little secret” comment at Madison Square Garden6:20AP on Mike Johnson aligning tightly with Trump and preparing a 100-day agenda and contested-election posture6:22Vanity Fair on Trump & Johnson’s “little secret” and fears of exploiting the 12th Amendment for 2024