President Trump sought to sharpen what he views as a threat aimed at sanctuary cities and states the other day, tweeting that undocumented immigrants “who can no longer be legally held” would be “given” to such jurisdictions.

The president didn’t single out any of the California’s sanctuary cities and counties, although he did take a swipe over the weekend at Oakland Mayor Libby Schaaf for calling the idea “an abuse of power and public resources.” It also wasn’t clear what he meant by his latest tweet Monday or how it would be carried out — Chronicle Washington correspondent Tal Kopan reported that there are several potential legal and practical obstacles to such a plan, which might be self-defeating for Trump anyway.

Those Illegal Immigrants who can no longer be legally held (Congress must fix the laws and loopholes) will be, subject to Homeland Security, given to Sanctuary Cities and States! — Donald J. Trump (@realDonaldTrump) April 15, 2019

But Trump’s style isn’t necessarily to carry out his tweet threats — in some cases, he seems mainly to be trolling the other side. Here’s a brief history of Trump’s tweets at California and what, if anything, they have led to:

The tweet: “California now wants to scale back their already failed ‘fast train’ project by substantially shortening the distance so that it no longer goes from L.A. to San Francisco. A different deal and record cost overruns. Send the Federal Government back the Billions of Dollars WASTED!” — Feb. 20, 2019.

California now wants to scale back their already failed “fast train” project by substantially shortening the distance so that it no longer goes from L.A. to San Francisco. A different deal and record cost overruns. Send the Federal Government back the Billions of Dollars WASTED! — Donald J. Trump (@realDonaldTrump) February 20, 2019

Background: California Gov. Gavin Newsom had just declared in his State of the State speech that there “simply isn’t a path” to build a high-speed rail line from San Francisco to Los Angeles, as has long been planned, and that California needed to concentrate on a Central Valley leg. Trump was demanding that California return the money the federal government has contributed toward the project.

What’s happened: In February, the Federal Railroad Administration said it intended to cancel $929 million in high-speed rail funding and that it was “exploring all available legal options” to claw back $2.6 billion that’s already been spent. The state responded in March that Newsom had not, in fact, killed the original plan and that pulling federal funding and abandoning the partially built train line would be “disastrous.” California’s High-Speed Rail Authority says it has not heard back from federal officials since then.

The tweet: “Billions of dollars are sent to the State of California for Forest fires that, with proper Forest Management, would never happen. Unless they get their act together, which is unlikely, I have ordered FEMA to send no more money. It is a disgraceful situation in lives & money!” — Jan. 9, 2019.

Billions of dollars are sent to the State of California for Forest fires that, with proper Forest Management, would never happen. Unless they get their act together, which is unlikely, I have ordered FEMA to send no more money. It is a disgraceful situation in lives & money! — Donald J. Trump (@realDonaldTrump) January 9, 2019

Background: As deadly wildfires burned in California in 2018, Trump said the state’s environmental laws were getting in the way of sound forestry management and making the disasters worse. Some forestry experts said Trump was oversimplifying a complex issue. Most of that back-and-forth played out in the fall, and it was never clear what prompted this dead-of-winter tweet.

What’s happened: Nothing, in more ways than one. The president never actively tried to cut off California disaster aid, but the $7 billion to $9 billion that the state would receive in a wide-ranging package is trapped in the Senate over objections by Trump and other Republicans it contains too much money for hurricane-racked Puerto Rico.

The tweet: “Governor Jerry Brown announced he will deploy ‘up to 400 National Guard Troops’ to do nothing. The crime rate in California is high enough, and the Federal Government will not be paying for Governor Brown’s charade. We need border security and action, not words!” — April 19, 2018.

Governor Jerry Brown announced he will deploy “up to 400 National Guard Troops” to do nothing. The crime rate in California is high enough, and the Federal Government will not be paying for Governor Brown’s charade. We need border security and action, not words! — Donald J. Trump (@realDonaldTrump) April 19, 2018

Background: Trump had asked California and other several other states to deploy their National Guard troops in response to an increase in asylum-seeking migrants at the southern border. Brown agreed to send California troops but said they wouldn’t enforce federal immigration law.

What’s happened: The day after Trump issued the tweet, the California National Guard said the Pentagon had approved federal funding for the mission as Brown described it. In March, new Gov. Gavin Newsom ended the California Guard’s deployment.

The tweet: “I have decided that sections of the Wall that California wants built NOW will not be built until the whole Wall is approved. Big victory yesterday with ruling from the courts that allows us to proceed. OUR COUNTRY MUST HAVE BORDER SECURITY!” — Feb. 28, 2018.

I have decided that sections of the Wall that California wants built NOW will not be built until the whole Wall is approved. Big victory yesterday with ruling from the courts that allows us to proceed. OUR COUNTRY MUST HAVE BORDER SECURITY! — Donald J. Trump (@realDonaldTrump) February 28, 2018

Background: Trump issued this tweet in response to a judge’s ruling that the administration could waive environmental laws for construction of border-wall prototypes. It was never clear which sections California supposedly wanted built; politicians in the state are not exactly clamoring for its construction.

What’s happened: The wall remains a subject of fierce debate.

The tweet: “If U.C. Berkeley does not allow free speech and practices violence on innocent people with a different point of view — NO FEDERAL FUNDS?” — Feb. 2, 2017.

If U.C. Berkeley does not allow free speech and practices violence on innocent people with a different point of view - NO FEDERAL FUNDS? — Donald J. Trump (@realDonaldTrump) February 2, 2017

Background: Trump tweeted out this threat one day after right-wing provocateur Milo Yiannopoulos’ attempt to appear before a conservative group at UC Berkeley was cut short by a riot outside the campus venue.

What’s happened: The administration has made no effort to limit the $400 million-plus that UC Berkeley receives in federal research funding. In March, Trump signed an executive order directing public universities to uphold the First Amendment, which they already must do to receive federal student aid or participate in other U.S. Department of Education programs.

Trapper Byrne is The San Francisco Chronicle’s politics editor. Email: tbyrne@sfchronicle.com. Twitter: @trapperbyrne