Most of 2018's midterm winners spent more money than their opponents. But some, like Texas senator Ted Cruz and incoming freshman congresswoman Alexandria Ocasio-Cortez, pulled out victories despite being outspent.

Why it matters: Candidates who outspend their opponents usually win. But some political obstacles are so large, even money can't overcome them.

In the Texas Senate race, Democratic challenger Beto O'Rourke, propelled by record fundraising for a congressional candidate, reported net expenditures of $55 million as of the final pre-election filing deadline — about twice as much as Cruz reported spending.

It wasn't enough to persuade Texas voters, who have not elected a Democratic senator since 1988. O'Rourke came close, with 48% of the popular vote — more than Hillary Clinton's 44% in 2016.

In Missouri, incumbency and a 4 to 1 spending advantage were not enough to save outgoing senator Claire McCaskill.

McCaskill spent about $32 million against challenger Josh Hawley's $7 million.

against challenger Josh Hawley's $7 million. Yet Hawley benefited from his popularity with rural voters and McCaskill's opposition to the nomination of Brett Kavanaugh to the Supreme Court. Hawley won with 52% of the popular vote.

While most of the outspent winners were Republicans — a side effect of Democrats' significant fundraising advantage — 11 Democrats managed to win their races while spending less than their opponents.

29-year-old Alexandria Ocasio-Cortez was outspent by outgoing congressman Joe Crowley in New York's 14th district. Yet Ocasio-Cortez beat Crowley and is getting ready to take his House seat in January.

Go deeper: