First time investing $100k into a Vanguard ETF for retirement — could a potential US–Iran conflict affect my entry timing?

I’m planning to make my first long-term investment for retirement by putting around $100k into a Vanguard ETF. My intention is to hold this position for many years, not trade short term. However, I’ve been watching prediction markets like Polymarket, and right now they’re pricing roughly a 70% probability of a US strike on Iran before January 31. My question is about short-term market impact and timing. If something like that were to happen, would you expect a broad Vanguard ETF (for example, total market or S&P 500 based) to drop noticeably in the short term? Or is this the kind of geopolitical risk that markets tend to absorb quickly unless it escalates into something much larger? I’m not trying to time the market perfectly, but since this is my first six-figure investment, I want to understand whether waiting for clarity makes sense or if this kind of risk is usually noise for long-term investors. I’d appreciate perspectives from people who’ve invested through past geopolitical shocks. One additional concern I have is whether it makes sense to wait and see if this potential event actually happens and enter after a possible dip. At the same time, there’s the risk that nothing materializes and the market continues to move higher, meaning I could end up buying 1–2% higher after waiting a month. Since this is a long-term retirement investment, I’m trying to weigh the psychological comfort of “buying the dip” against the opportunity cost of staying on the sidelines for a few weeks. Curious how others here think about this kind of trade-off when deploying a large lump sum for the first time.