The 'Trump Rally' in the stock market is hitting multi-decade records.
This is from last week.

The stock market is having its best performance in the first month of a rookie president's term since the 1960s.
The S&P 500 has gone up 3.8% since Trump took office.
That's the biggest increase for a new Republican president since the blue chip index that eventually became the S&P 500 debuted in 1923, according to S&P DJ Indices.

And this is from yesterday.

The red-hot Dow closed at an all-time high yet again on Monday, its 12th consecutive record day.
That's only happened two other times in the 120-year history of the Dow. There has never been a 13-day streak of records, though that could change on Tuesday.

The euphoria of investors in a new presidency is something to behold. I've never seen this in my lifetime.
It begs the question, "who are these people?"
Bloomberg has an answer.

After years of snubbing the asset class in favor of fixed income, retail investors are showing pent-up demand for stocks amid an escalation in risk-taking and projections for economic growth since the November election.
From the $86 billion plowed into equity exchange-trade funds so far this year, Panigirtzoglou and team calculate that 2017 as a whole may see equity funds absorb a net $442 billion of new retail-driven money if the year-to-date pace is sustained. That would be almost six times larger than last year’s volume, according to JP Morgan.
On the other hand, institutional investors from risk-parity to mutual fund managers have decreased their exposure to the equities, the team concludes from assessing various active managers’ returns -- another sign that the flows to passive strategies are likely dominated by retail investors.

In other words, professionals are selling stocks while amateurs are buying them.
Normally that would be enough information, but this isn't normal times.
I can get more specific than that.

When it comes to confidence in the U.S. economy, the partisan divide is the widest ever on record. Democrats are expecting an outright recession, whereas Republicans are expecting the exact opposite–and getting ready to let the boom times roll.
The latest figures released by the University of Michigan Surveys of Consumers on Friday show sentiment among Republicans was 120.1, in line with expectations for robust economic growth, whereas it was only 55.5 for Democrats – a number predicting recession. The gap between the two is the widest on record, since the study started in 1945, according to Richard Curtin, who compiles the survey.

Since people who are "expecting an outright recession" don't normally buy lots of stocks when the market is at an all-time high, the answer for "Who's buying the Trump Rally?" is "Trump Fans".
It really is as simple as that. Which gives a whole new definition of "Dumb Money".

Let's not stop there, because stocks aren't the only thing hitting all-time highs.
Home prices are above the housing bubble peak price, with home sales at their highest levels since February 2007.
So who is buying these homes at nosebleed prices?

Last year, 37 percent of homes sold were acquired by buyers who didn’t live in them, according to tax-assessment data compiled in a new report published by Attom Data Solutions and ClearCapital.com Inc.
In the years following the foreclosure crisis, Wall Street drove a rise in the share of homes purchased by landlords, as private equity firms bought thousands of cheap homes. In 2012, institutional investors accounted for 7.8 percent of home sales, according to the report.
Rising home prices led big investors to curtail their purchases, and the share of homes acquired by institutional investors fell to 2.9 percent last year. But as Wall Street backed off, smaller investors picked up the slack, aided by tools developed to help big investors find, finance, and manage rental properties.

Once again, the professional investor is not buying, but the amateur is buying at all-time high prices.
Once again, normally that would be enough information, but this isn't normal times.
I can get more specific.

During the last week of October, when Hillary Clinton was ahead in the polls, Trulia commissioned surveys of 2,000 Americans. Respondents who identified themselves as Republicans said that 2017 would be worse than 2016 for selling a home, buying a home, getting a mortgage, or finding rental housing. Democrats thought that 2017 would be better in each of those categories. After Donald Trump’s surprise electoral college win, outlooks for Republican and Democratic respondents flipped—in every category.
“It’s really not very intuitive,” said Ralph McLaughlin, chief economist at Trulia. The second survey, for instance, was conducted after mortgage rates spiked in response to the election results. “Even if your side wins, if mortgage rates go up, you might get pessimistic about your chances of buying a home.”
These are dramatic swings, and it’s tempting to attribute them to an emotional response following a result that caught most people by surprise.

Since people who think it's a bad time to buy a house don't normally buy houses when prices are at an all-time high, the answer for "Who's buying these houses?" is "Trump Fans".
Again.