(CNN) It's been almost 140 years since a US president didn't veto something during his time in the White House. And that President, James Garfield, was assassinated before he could serve a full year in office in 1881.

If Senate Majority Leader Mitch McConnell keeps blocking for President Donald Trump, then he could be the next.

It's true that George W. Bush served a full four-year term without issuing a veto, but he made up for lost time in his second term, especially when Democrats took control of Congress and the Senate in 2007.

Bush also never stared down Congress to cause the longest partial government shutdown in US history like Trump has in recent weeks.

As the government shutdown nears the month marker and after a number of Republican senators have expressed a willingness to fund the government despite Trump's demand for money to build a border wall, it's worth exploring whether and how Congress could fund the government without him.

Note: At this point, the discussion is completely academic since McConnell has said he won't allow a vote on any bill the President doesn't support. McConnell, for now, controls the Senate floor and as long as the Senate Republicans carry water for the President, he won't have to veto anything.

That said, here's how the veto and veto override process works. Bookmark it for if and when there are developments in this shutdown standoff.

Can a bill get to Trump's desk? Not yet.

The government is funded by appropriations bills approved by both the House and the Senate and presented to the President.

For a spending bill to reach Trump's desk, the House, which is controlled by Speaker Nancy Pelosi and the Democrats, would have to pass funding legislation that at least 13 Senate Republicans would support. In order to overcome a likely filibuster by senators who support the President, any legislation would need a 3/5 majority, or 60 senators if everyone is voting. There are 53 Republicans, 45 Democrats and 2 independents who vote with Democrats. Only three Republican senators have suggested they'd support appropriations the President opposes. So that seems a long way off. Check back in when at least 10 more Republicans have said they would break with the President and their party. They'd also have to find a way to get McConnell to bring the bill to the floor.

What are Trump's options if a spending bill gets to his desk? Sign, veto or Ignore.

Trump can either sign a bill the House and Senate send to him, making it law, ignore it and after 10 days it becomes law without his signature, or he can veto it, sending it back to the House and Senate. One other possible scenario is the pocket veto, which occurs if the President doesn't sign a piece of legislation passed by both chambers and the House and Senate adjourn, in which case the bill would be essentially vetoed.

But that's not the end of it. Vetoes can be overridden by a 2/3 supermajority vote in both chambers on Capitol Hill. In the House, Democrats have 235 seats and Republicans have 199 and there's one vacancy. That means Democrats would have to pick up 55 House votes to get to 290 votes and a 2/3 majority if everyone votes. In the Senate, they'd need to pick up 20 Republican votes.

Pocket vetoes cannot be overridden, but the legislation would have to be reconsidered when Congress reconvened.

What if Trump vetoes a spending bill? Override?

Vetoes occur more often than you might think. Every president since Garfield has vetoed at least one bill. The younger Bush was the first president since John Quincy Adams to go a full four years without a veto, according to the Congressional Research Service. Barack Obama, similarly, had help on Capitol Hill for most of his presidency, just as Trump has.

The President with the most vetoes was Franklin D. Roosevelt with 635, although he also served the longest in the White House. All those vetoes came even though Roosevelt enjoyed Democratic majorities for his entire time in the White House.

In fact, if you plot vetoes alongside how closely aligned Congress is to the president, it is not rare at all in US history for a president to veto bills from a House and Senate aligned with him. This data comes from The American Presidency Project at the University of California at Santa Barbara

But that's changed in modern history. If you look only at vetoes since 1972, when Richard Nixon faced a Democratic Congress, most of the vetoes have come when at least one chamber was not aligned with the President. That's how Bush went four years without a veto. The House, which was Republican for his entire first term, was protecting him from bills he opposed.

Veto overrides are much more rare than vetoes. There have been only 111 in the history of the country, but they have impact.

One of the country's few impeachments, Andrew Johnson's, was precipitated by a veto override

In more recent history, the Freedom of Information Act and Clean Water Act were both passed despite presidential veto. The last time an appropriations bill was overridden was during Ronald Reagan's administration, according to The American Presidency Project