Democratic presidential candidate Bernie Sanders said Sunday that he will continue his challenge to front-runner Hillary Clinton even at the party's convention in July.

"The convention will be a contested contest," Sanders said at a Washington, D.C. press conference Sunday.

Sanders' pledge to push superdelegates behind Clinton to support him during the nominating contest raises the chance the Republicans' Cleveland gathering will not be the only convention fight this summer.

Sanders received four big blows in last week's five primary races, losses that reduced to nil his ability to win the 2,283 delegates necessary to secure the nomination without a brokered convention.

But Clinton is also at a disadvantage, Sanders says.

"It is virtually impossible for Secretary Clinton to reach the majority of convention delegates by June 14 with pledged delegates alone," Sanders said, referring to the final day of primaries. "She will need superdelegates to take her over the top at the convention."

That's where Sanders said his campaign will attempt to further complicate the front-runner's effort. He hopes to steal superdelegates already committed to her, including some who backed her before Sanders announced his bid last April.

For Sanders the fight may be less about winning the election than earning support that he believes is rightfully his. He complained Sunday about primary rules, including a rule imposed by New York Democrats that barred independents from voting in the state's crucial primary, won handily by Clinton.

Clinton has won 55 percent of the pledged delegates and Sanders has secured 45 percent. The democratic socialist would need an additional 710 pledged delegates or 65 percent of the remaining delegates to lock down the nomination before Philadelphia, which is where superdelegates become very useful.

But Clinton and Sanders have 520 and 39 superdelegates, respectively. Sanders blamed the party establishment for backing its "anointed" candidate as the reason he has only been dealt 7 percent of superdelegates.

"I would hope very much that the superdelegates from those states where we have won with big margins would respect the wishes of the people of those states and vote in line with how the people of that state voted," Sanders said.

He's banking on what Democrats have chided Republicans about for months: a nasty fight on the convention floor to win on technicalities.

His argument for superdelegates is simple. Polls of hypothetical general election match-ups show him defeating Republicans more easily than Clinton.

"The evidence is extremely clear that I would be the stronger candidate to defeat Trump or any other Republican. This isn't subjective evidence of Bernie Sanders. This is what the polls say," Sanders said, pulling out Morning Consult poll figures from the podium.

Clinton backers and other analysts argue that such polls are worthless before the general election contest. They argue that Sanders' numbers are inflated because he has faced little negative advertising in the race so far. In a general election that would change dramatically.

Sanders has won 17 state primaries of the 40 and hopes to make a dent in the remaining 10, as well as Washington, D.C., Guam and the Virgin Islands. His first test in the uphill battle will be Tuesday when Indiana residents hit the polls.