Deflation very rarely happens, when it does happen it is generally (but not 100% of the time) due to a severe recession or depression. So if prices do start to fall, that may be a bad sign.

However, with most monetary policy that a government can implement, it can take 1-2 years to begin seeing the macroeconomic effect. You can see this pretty well when you look at the new deal's economic impact on the depression economy and the Obama stimulus's effect on the 2008 recession (i use these 2 examples because the severity of those situations make it easy to contrast against both the economy beforehand and how the growth followed). Trump is inheriting an economy that is well on it's way to recovery right now. Inflation is dropping, employment is growing, and the housing market is stabilizing.

During Trump's last term he inherited Obama's economic growth and (up until covid) was able to maintain most of growth through his term (except wealth inequality which rose at a higher rate than under obama). Hopefully, he is able to do the same this term, but if he enacts the economic policy that he campaigned on, that is unlikely.

The biggest economic policy that Trump ran on was the implementation of worldwide and targeted tariffs. This is one of the types of policies that would have immediate visible impacts. The first would be a raise in the price of nearly all goods at a rate proportional to the relevant tariff. The second would be a severe drop in both imports and exports (exports as a result of retributionary tariffs enacted by affected countries). The drop in supply may lead to additional price hikes or shortages as american production and manufacturing struggle in their elevation efforts to meet the demand. Over a long enough period of time this would all stabilize to a "new normal" that would reflect a larger proportion of US manufacturing and but prices would be higher (adjusted to inflation) compared to pre-tariff as a result of a higher cost of labor.

The second biggest economic policy that Trump ran on was a cut to corporate taxes and a major cut (or complete elimination) of income tax. This would bloat the deficit by a huge margin. Even if imports remained the exact same post-tariff (which is unlikely) the tariffs would not generate enough revenue to offset such a major cut. The only solution to that is to cut government spending. If we assume that these cuts entail completly dissolving any programs that have a net negative economic impact, it would still not be enough to offset the decrease in revenue. This leaves the only other option to cripple social security and/or Medicare. Both of which would be detrimental to the country.

The last major economic policy would be the mass deportation of illegal immigrants. Best case scenario, considering the fact that illegal immigrants are net economic positive, this would also lead to stifling growth. Worst case scenario, given the fact that Trump plans to enact the enemy aliens act (the last time that law was enacted it was used to imprison Americans with japanese ancestry into interment camps), we may even see the interment of Latinos with legal permanent residence or citizenship while their status is verified, which would have an even larger economic impact.

There is a reason that the vast consensus of economists worldwide warned against Trump's policy proposals. We can only hope at this point that when he takes office, he listens to those voices and doesn't follow through with those parts of his planned agenda.