US PRESIDENT Donald Trump has threatened he will be willing to shut down the government if Democrats refuse to vote for changes he seeks to make to the US immigration system, including building a wall along the US-Mexico border.

“I would be willing to ‘shut down’ government if the Democrats do not give us the votes for Border Security, which includes the Wall!” the president tweeted.

“Must get rid of Lottery, Catch & Release etc. and finally go to system of Immigration based on MERIT!

“We need great people coming into our Country!”

Mr Trump returned to the idea of shutting down the government over the border wall just days after meeting at the White House with House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell to discuss the fall legislative agenda.

Mr McConnell, asked about a shutdown last week during a Kentucky radio interview, said it was not going to happen.

He did acknowledge, however, that the border funding issue was unlikely to be resolved before the November midterm elections.

Mr Trump campaigned on the promise of building a border wall to deter illegal immigration and making Mexico pay for it. Mexico has refused. Congress has given the president some wall funding but not as much as he has requested.

Mr Trump also wants changes to legal immigration, including scrapping a visa lottery program. In addition, he wants to end the practice of releasing immigrants caught entering the country illegally on the condition that they show up for court hearings.

The president has also demanded that the US shift to an immigration system that’s based more on merit and less on family ties.

Democrats and some Republicans have objected to some of the changes Mr Trump seeks. The federal budget year ends on September 30, and politicians will spend much of August in their states campaigning for re-election in November.

The House is now in a five-week recess, returning after Labour Day. The Senate remains in session and is set to take a one-week break the week of August 6, then returning for the rest of the month.

Both chambers will have a short window of working days to approve a spending bill before government funding expires.

Mr Trump would be taking a political risk if he does, in fact, allow most government functions to lapse on October 1 — the first day of the new budget year — roughly a month before the November 6 elections, when Republican control of both the House and Senate is at stake.

House Republicans released a spending bill this month that provides $US5 billion next year to build Mr Trump’s wall, a major boost.

Democrats have long opposed financing Mr Trump’s wall but lack the votes by themselves to block House approval of that amount. However, they do have the strength to derail legislation in the closely divided Senate.

Without naming a figure, Mr Trump said in April that he would “have no choice” but to force a government shutdown this fall if he doesn’t get the border security money he wants.

The $US5 billion is well above the $US1.6 billion in the Senate version of the bill, which would finance the Homeland Security Department.

The higher amount matches what Mr Trump has privately sought in conversations with Republican politicians, according to a GOP congressional aide who wasn’t authorised to publicly talk about private discussions and spoke on condition of anonymity.

Two leading Democrats — Nita Lowey of New York and California’s Lucille Roybal-Allard — called the $US5 billion a waste that “only further enables this administration’s obsession with cruel attacks on immigrants.”

TRUMP SAYS HIS NUMBERS ARE HIGHER THAN LINCOLN’S
Separately on Sunday, Mr Trump tweeted his poll numbers are higher than “Honest Abe Lincoln” despite the fact that presidential polling didn’t begin until 1936.

It’s unclear which survey he was referring to, but Gallup became the first company to poll a presidential election in 1936, according to the New York Post.

The publication reports a survey released last month found Trump’s approval rating was at 42 per cent and his disapproval rate at 54 per cent.

Comparing Ronald Reagan’s numbers at the same point in his presidency, Gallup found Reagan’s approval rating also at 42 per cent.

Among other Republican presidents in July of their second year, George W. Bush had a 72 per cent approval rating and George H.W. Bush had a 62 per cent approval mark.

But Republicans gave Trump an 88 per cent approval rating, compared to 9 percent among Democrats.

On Sunday, Mr Trump also tweeted that there are “consequences when people cross our Border illegally”.

His tweet came several days after the government said more than 1800 children separated at the US-Mexico border under Mr Trump’s “zero-tolerance” immigration policy have been reunited with parents and sponsors.

A federal judge had ordered the reunions to be completed by last Thursday but hundreds of children remain separated.

The administration says some of their parents have criminal histories.